Cory, always take the biggest pictures your camera (and memory card(s) can take). There are tons of apps out there that can very easily resize pictures to a more web-usable size. If you take smaller pics and ever want to print one or to use as a desktop picture, you're stuck with a small photo that can't get bigger without reducing quality.
I don't know what kind of camera you have, but the higher end cameras will likely have the RAW photo format. Creates huge files, but are highly flexible. If you happen to use a Mac, I highly recommend checking out Aperture.