WOW this thread took an off topic turn and FAST!
Sue, every response assumed running an alternate operating system off of a memory card, but my guess is that you simply want to expand storage capacity. If that is the case, it changes the methodology a great deal in your favor.
Clarification: all that talk about the class number is for the most part only relevant if you are running an alternate android version such as nook2sd or another version of CM7running off the card. The only other factor to consider the class number for would be the read/write speed. The higher the class, the faster you should be able to transfer files to and from the card. If you don't mind waiting 5 minutes for a movie file to transfer to your sd card, there is no reason for the class number to be a considered factor. Since the standards for the class numbers are set by the manufacturers, at least as I understand it, comparing class numbers of different brands is pointless anyway.
Simply put:
If you want to run an alternate android version, use a sandisk class 4, at least 4gb.
If you just want a place to keep your ebooks, PDF's pics, word documents, and movies, buy whatever is on sale. Just make sure it's a MICRO sd.
PS--- CM7 is not optimized for low speed SD cards. Good luck getting it to work on a class 2. It is pure happenstance that it works the best (for most people) on a sandisk class 4. This is an important distinction to make for the CM7 do-it-yourselfer.
