Depends on the type of photography you will be doing. If it will be the type that requires the use of high speed continous shooting, then you're going to need the fastest possible card to allow the fastest write to the card. If you will be taking single shots at a time, then the write speed is not so much of a factor, and then you can go with the slower, and therefore cheaper cards. How big the size of the card, 4meg or 8 meg etc, is personal preferance.
Myself, I shoot a lot of air displays and aviation, so can sometimes need the fastest write speed. Size of card, I prefer 8meg cards, which give me 304 pics on the card shooting in RAW. My preference is not to go for larger, just in case the card becomes damaged/lost etc, then I have only lost 300 pics, not possibly double that with a 16meg card. I also have a bunch of 4meg for precisely this reason. I use Sandisk cards, as they have proved reliable for me in the last couple of years.
All the above advice is free, therefore if I'm wrong, too bad
Chris