I have personally assembled several camera systems for myself, friends, local business's and schools.
it can be very expensive, confusing, and ineffective if you don't know what you are doing.
*First off, you need to decide whether you want your cameras inside, or outside. 
Indoor cameras minimize  vandalism of the camera itself, and aren't as conspicuous as outdoor cameras. However, this will limit sounds from outside, and  most nightvision cameras dont look through glass very well, (you will only get a big reflection).
**An important fact  to remember is *big price tag doesnt mean better cameras*. in my years of doing this, I have never bought a ridiculously high priced name brand camera that i was satisfied with. The China-made ones you can find on ebay for 30$ are quite comparable to the ones you can find in electronics stores for hundreds of dollars.

*What is BNC, RCA, DIN, etc? that refers to the fixture on the end of the cable that is coming from the camera. You must make sure that your camera, cables, switches, and monitor are all the same.    BNC  resembles  the cable for television. RCA are the red, white, and yellow cords on your VCR.  and DIN are the ones on your computer that you screw in( like your monitor). DIN can also resemble S-video cabe.  i prefer RCA because of its almost universal connectability.
BNC:                        RCA:                          DIN: Or
*adapters are available*

*Always OVER-Esimate how many feet of cord you will need. if your camera is 50 feet from your monitor, you may need well over 100 feet of cable. You must consider how you want them concealed as well as  any obstacles they will have to go around.
*If you opt for outdoor cameras make sure they say "weather Proofed" and not "weather  Resistant", the difference is self explanatory.  Also make sure that they can run in your local climate; a rainforest might require water proof cameras, alaska would require cameras that can function in subzero, and many plastic cameras will melt in Californian sun.

*Also, you must consider how you want your cameras displayed and recorded. you can have them simultaneously on a split screen, or in intervals where the view is rotated from one camera to the next. "split displays" are more expensive than "video switchers".    DVR's are the way to record; video cassettes wear out, look crappy, and always let you down. 

*What is IR and LED? IR stands for "infra-red" and LED's are lights. Infra red is invisible to humans, not to cameras. 12 IR LED means the camera has 12 Infra Red Lights for night vision. I like this form of nightvision, very affordable, you can buy infrared spot lamps or "illuminators" for added brightness.
 this is an inexpensive "illuminator" *note: IR light is invisible to humans, it only Illuminates for your night vision camera

Pan Tilt and Zoom (or PZM's) are cameras that can look side to side(pan), up and down(tilt) and zoom in. Many can even be setup to do combinations of the above, repetitively.  I do Not like PZM because it leaves open spaces. where as one or two well placed, regular cameras can have an equally commanding view, without the occassional unmonitored gaps. They are also Incredibly expensive.
Here are some diagrams explaining the views of the cameras.
The square is what you want to protect(your house) the triangles represent what the camera can see. 

As you can see in this example of a PZM, there are huge gaps where someone could sneak up and disable the camera.



This setup, is great for a large field of view, the downside is that once the perimeter is broken, there is a large unmonitored gap in between the cameras. and they too can be disabled.

This is the most effective setup. as you can see, the front of the "house" is completely in view. and each camera covers the other. you cannot approach one from behind without being caught by the other camera. i love this setup.
 the cameras can also be placed back to back, in the center, just as effectively.


For Specific suggestions on cameras I like the "36 IR LED" cameras which are very cheap and very effective. they are always on ebay for 10 to 20$
 I like Pelco, which is more on the expensive side, but they have great computer based systems, with excellent software. if you want to really be secure, and spend lots of money on it, pelco is the way to go.
Lorex is a good brand that is pretty affordable, however Some of there products are a little flimsy.  They do have great "all in one" kits though, with monitor, cameras, and cable included.
key terms:  "split quad display" "video switcher" "BNC" "RCA" DIN"  "pan tilt zoom" "36 ir led " "illuminator" "DVR"