Some of the things you should know about cards have been said. I can't agree more on the anti-microdrive statements. For the money saved your increasing risk to your card and losing images, moving parts...bad.
As far as memory, bring it down to which camera you have, what kind of shooting. In some cases I would suggest pro level cards with image recovery software, in others you can look at with less write speed so that you can save some pennies.
All in all, CF is the most cost effecient memory out there on the market today.
if you want drop me a line and we will chat memory cards that work best for your 6mp camera
Sandisk and Lexar are generally the best ones out on the market
Glorified Unique Photo Counterboy