Alright, so you want to get into the world of airsoft, but don't know what exactly you should purchase. Many beginning players make the mistake of purchasing the cheapest guns they can find, and pay for it in the field when their LPEG's and whatnot fall apart. As someone who has been involved with the hobby for quite some time, I have a few tips to offer:

Sample loadout. Note ESS Land Ops goggles, Blackhawk STRIKE harness with pouches, Alta kneepads , TM M733, etc.

First off, the most important purchases:

1) Paintball masks or full-sealing goggles (ANSI 287.1 is a recommended standard by many, though there is debate over it.) Safety is a critical part of the game, and if you don't take the precautions necessary to keep your eyes intact, you probably shouldn't be playing the game. Be cautioned against mesh airsoft masks, as they have the potential to shatter and ruin your eyes. In addition, you may want additional protection for your face if you have not invested in a full paintball mask, such as a shemagh, though this is optional for the most part (in close quarters you will definitely appreciate the facial protection, for example.) Manufacturers of tactical goggles that can be used for airsoft purposes include Bolle, ESS, and Wiley. Note that no eye protection system is completely fog-proof, so you should look into anti-fogging solutions, ranging from ESS Turbocam fans to simple anti-fog wipes.

2) A primary gun. For a primary weapon you should order an AEG (automatic electric gun) manufactured by Tokyo Marui if you are just starting out and do not know the workings of AEG internals. Other than TM, Classic Army has slightly more powerful but less reliable guns (reports indicate their quality control is improving,) Systema has expensive but well worth it PTW's, and ICS and G&P weapons have suspect internals. Other higher end manufacturers include VFC, G&G, and STAR, which make guns of varying quality. I'm not exactly knowledgeable on the subject of gas pistols or spring/gas-powered sniper rifles, other than they should not be your primary weapon when you are starting out in airsoft - you should get a feel for how the game is played with standard weapons first, before moving on to more specialized tasks and weaponry. If you are certain that you can fill a role effectively, then I suppose you can get the particular weapon platform that you desire.

More recently, Echo 1 (primarily rebranded Jian Gong, Kart, and other manufacturers) guns have hit the AEG market, and seem to be a bargain for the price you pay - they are inspected to ensure some degree of quality, and come with 30-day warranties. Other low-end manufacturers are also making gains in quality: CYMA, JG, UTG, etc. These companies may be worth checking out as a cheaper manufacturers (though their products have their share of problems, given that they're cheaply made to be cheaply sold.) Most other makers in the low-end, should be cautioned against for the most part. Even the highest end guns are not free from problems, as the STAR M249 is notorious for its unreliability and the initial batches of G&G guns had various problems. The gist of this long paragraph is that there is no perfect AEG, but Marui makes solid, dependable products that should last a long time, ideal for a beginning player. The Marui M733 I bought five years ago is still running perfectly fine today, tens of thousands of rounds later.

Skirmish-worthy AEG's

3) Necessary accessories for your primary. If you have an AEG, you will want at least one battery to power it. Make sure to buy a battery (NiMH or NiCad*) with the appropriate voltage, usually 8.4V for stock TM weapons, 9.6V for guns that shoot at higher velocities (350+). Also be sure that it will fit on or into your weapon, unless you have a battery bag, redimag, crane stock, or some other form of external storage. Your battery will also require a charger, look into a peak-detecting charger. If you are using a gas-powered airsoft gun, you will want HC134A (duster gas is a good substitute) for stock Japanese guns such as KSC, Western Arms, and Marui, and HFC22 (green gas) or propane as a substitute for most other GBB's made in Taiwan (KJW, KWC, KWA, etc.)

4) BB's. Please buy high quality bb's for high quality AEG's. Recommended manufacturers include Excel, Airsoft Elite, Tokyo Marui, Stealth, and several others. Remember to purchase enough to last a few games, rather than risk running low during a skirmish.

Alright, so you have the most basic equipment necessary. Now for other equipment, purchase at your own discretion.
Other Gear:

- Camoflauge. Depending on your location, you should get the right set of BDU's (Battle Dress Uniform): US woodland, 3-color desert, British DPM, etc. Check out eBay stores for low prices on army surplus items. Beyond your one basic set, you can invest in more BDU's if you wish, whether they are for uniform requirements at certain games, to loan out to friends on occasion, or simply because you think they look cool.
- LBV/LBE/chest harnesses/assault vests/etc. There is a plethora of gear in this area, one of your cheapest but surest options would be army surplus LBV or LBE (ALICE) equipment. In general, these rigs will allow you to carry extra magazines and other accessories you may have, such as radios, and may cost up to $50 for a complete setup (ex. a LBV, pistol belt, and two canteens.) The next step up would be tactical vests, such as the Blackhawk Omega series. If you are willing to spend enough money to be considered a "geardo," I would recommend American manufacturers that actually make their items in the States, such as Tactical Tailor, Eagle Industries, Paraclete, etc. Much of this gear has actually been deployed out in the field, such as the Eagle CIRAS (Combat Integrated Releasable Assault System) used by SOCOM: if it suits a soldier, it can suit an airsofter. Modular gear, usually of the MOLLE standard, is recommended since you can configure your combat loadout however you please.
- Additional magazines for your gun. One standard magazine is not enough to last a whole battle (perhaps in CQB,) while high capacity (hicaps) magazines will fare better; midcap magazines fall somewhere in between. If you are just starting out, invest in a spare hicap or two as mass purchasing standard magazines can get expensive. It is recommended that players looking for a more realistic approach to playing airsoft begin investing in low capacity (usually of the STAR 30-round variety) or standard magazines for AEG's.
- Hydration. It doesn't really matter what form it is in as long as you can add it to your loadout (nalgene bottles, canteens, camelbaks, hydration carriers, etc.) As Camelbak's expression goes, "hydrate or die!"
- Footwear. Boots are key for comfort out in the field, though you can use shoes at your own discretion.
- Other gear. Miscellaneous gear include hats, helmets, kneepads, tactical gloves (such as of the Nomex flight glove variety,) balaclavas, etc.
- Communication gear. Most airsofters use FRS /GMRS radios, usually of the Motorola Talkabout variety or other similar models. You will also want to invest in an earbud, throat mic, or similar accessory.**
- Spare guns. This category is pretty open - you can opt for backup AEG's, gas pistols as backup weapons, high powered sniper rifles (costing at least $150,) etc. I just recommend a stock TM AEG as your primary gun if you are a newbie getting into the sport, and expand your loadout from there.
- Miscellaneous. Compasses, watches, RIS/RAS systems and other weapon accessories, weapon upgrades (such as springs and metal bushings,) flashlights, scopes, etc.

Hopefully, this is enough information for players starting out. If you have further questions, visit large airsoft sites and check for internet forums based in your local area. Some sites to check out include Airsoft Core, Airsoft Retreat, Airsoft Players, and Arnie's Airsoft in the UK.

Additional Notes:

It has been said that airsoft is 90% looks, which rings rather true since most guns share similar internal components. When you are shopping for a gun but can't decide what to get, go with what YOU think looks coolest. Everyone's opinion is different, so it would be very hard to get an objective answer when querying people's opinions of how certain models look.

Airsoft is expensive, but there are ways to cut costs. An example of a more economical outfit would include paintball mask, AEG, a hi-cap, battery, battery charger, and perhaps surplus BDU's. Used products in general will be cheaper than their brand new counterparts.

Purchasing on eBay:
1) Read the item description thoroughly. If a deal sounds too good to be true, say $40 for a TM MP5, it probably is. If however, after careful reading, it does actually appear to be a good deal, then by all means go for it.
2) Don't cheap out too much, a good quote for this hobby is "you get what you pay for." Although it is good to save money, say, on used magazine packages, there are other investments you should make for the long run, such as a good peak charger for your batteries to prolong their lives.

Footnotes
* There are Li-Poly batteries on the market now, I have very little experience with them so I would recommend that you research their capabilities before you decide to make a purchase in that area. There is also a degree of danger to using them, as they may light on fire if their protective covering is somehow punctured.
** One basic tip for airsoft communication is to avoid VOX, it is too sensitive to even the slightest of sounds and will most likely flood the channel with your breathing and movement. If you have an earbud, make sure it's of the PTT (push to talk) variety, or compatible with the PTT button on your radio.