The best setup would be a one DVDplusminusRW drive and one DVDminusROM drive. the plusminusRW drive will be able to burn anything you want (DVDplusR, DVDminusR, DVDplusRW, DVDminusRW, CDR and CDRW) and the ROM drive will be faster at reading anything you want. Also with two optical drives you can make copies on the fly, instead of copying it to your HDD and then to a disc. It's not hard to find a good deal on a dual layer p-RW drive, so if you can, get that. You can still use all single layer media, and just start using the dual layer media when the price comes down some more (within a year or two it will be very reasonable). If this is just for data, and will only be used by you, make sure it has plus cpapbility which is often 2x as fast as minus.
Also keep in mind not all current dvd players will play all formats. It would be a good idea to get a plusminus drive and try both discs on your home dvd player (if your going to use this for movies that is). It would suck if you get a plus drive and your dvd player only does minus, or vice versa.
The best deals to buy PC parts online is
http://www.newegg.com and
http://www.outpost.com . Outpost sometimes has better deals than Newegg, but charges shipping on everything but Newegg often has free (or very cheap) shipping to CONUS. You will probably get a better deal online that in a store.
There are 10 kinds of people in the world: Those who understand Binary, and those who don't.