It really depends on what quality you want. I'd recommend checking out this PDF document from SanDisk. It provides a quick guide to storage capacities for cameras between 2MP and 8MP and cards between 64MB and 2GB.
Note that most cameras use compressed mode by default, and that the exact capacity will vary a little by model. (I usually get 10%-15% more than the average)
Hope this helps,
How many pics can a 256 MB SD Memory card can hold? i have a Kodak EasyShare and I want to buy a memory card for it. How many pics will I be able to hold on a 256MB SD card?
Thanks for the help.