DVD stands for Digital Versatile/Video Disc,

DVDR stands for DVD Recordable. 
A DVDR (4.7 GB) stores up to 2 hours of very good quality.  If you choose to lower the video quality you can store much more on the DVDR.  Using lower quality recordings lower the bitrates and resolution.  On the screen of our portable DVD players the lower bitrates and resolution look great but not to good on the Big Screen.

DVDRW stands for DVD ReWriteable.  These discs are more expensive but great for if you want to reuse the disc for other things in the future.

Difference between DVD-R and Dvd+R?

Basically there is not any difference but you must check you DVD players for compatibility.

DVD-R was the first DVD recording format released that was compatible with standalone DVD Players. Also DVD-R is a non-rewriteable format and it is compatible with about 93% of all DVD Players and most DVD-ROMs.

DVD+R  is a non-rewritable format and it is compatible with about 89% of all DVD Players and most DVD-ROMs.  Most newer DVD players support this format also. 

When shopping for a DVD player most will support both formats.  It will have a symbol on the box that looks like this DVD+R

How much should I spend on Disc?

DVD-R and DVD+R are the cheapest format to buy as they are only good for one use.  I have used both Memorex, HP, Sony, and Staples brand with no problems. I think anywhere from .15-.29 cents each is a descent deal, you just need to price search, and buying in bigger quantity will save you some money too. Watch for sales also, Normally the HP DVD+R runs 58.00 or 59.00 bucks but Staples had a weekly deal where you can get a 100 pack for 24.98, I bought 2 of them for the price that one normally cost.

What’s the difference between DVD-RW and Dvd+RW? 

Basically there is not any difference but you must check you DVD players for compatibility

DVD-RW is a rewriteable format and it is compatible with about 80% of all DVD Players and most DVD-ROMs. 

DVD+RW is a rewritable format and is compatible with about 79% of all DVD Players and most DVD-ROMs.

What’s DVD-R DL or DVD+R DL?

DVD-R DL &  DVD+R DL stands for Dual or Double Layer Discs.  These are single use.
DVD-R DL is a Dual Layer writeable DVD-R. The dual layered discs can hold 7.95 computer GB (called DVD-9) and dual layered double sides 15.9 computer GB (called dvd-18 ).They are expensive in IMHO.  Alot of storage on these especially if you need to put alot on one disc.

What Speeds?
DVDs come in different speeds 2x,4x, 8x, 16x ect... The speeds you need to get depends on the speeds your burner will go to. For example my Philips 3455 recorder will record up to 16x speed, so it will burn disc up to that speed, so buying a 16x disc is what I would need. Now if your recorder only does 12x or 8x or even 4x, then buying a 16x disc is really not going to make a difference because it will only burn or record to the disc at the greatest speed the recorder will go. Now IMHO, I haven't noticed a big difference in the recording speeds of 4x or 8x, but 16x I can see that it is somewhat faster, but not that much. I've also noticed that when I do record to a 16x that it doesnt freeze like its done with the lesser speeds.
 
DVD-RAM
DVD-RAM is not compatible with most DVD-ROM drives and DVD-Video players. Think of it as a removable hard disk.