I just finished Genki 2 and am about to buy an Integrated Approach to Intermediate Japanese, but I'm not sure if I should get the "original version" (it has a black and red cover) or the revised edition? What's the difference besides the CDs?

You should probably get the one with the CDs, but beyond that, the language will just be a little more up-to-date probably.

Get the one with the blue cover (most recent edition). Supposedly they updated the readings to be more current and less painful to get through. AFAIK, it also comes with the CDs, not separately.

Good luck. Fair warning: There's a lot less English (no translations of dialogues or readings), though it does give you the vocab definitions and grammar explanations. I found the Dictionaries of Basic/Intermediate Japanese Grammar to be more helpful than their explanations though.