You can buy the MGMAT online, computer adaptive test bank for $39 from manhattangmat.com. They give you complete explanations for all of the questions from each test. You can take at least 6 tests without the questions being repeated, too.

I think that the old paper GMAT's are good for practice and timing, but taking a GMAT CAT would be more closely representative of the real thing. I would still take the other GMATPrep test from mba.com. Although those two GMATPrep tests don't come with any explanations, they are still good tests to take. You might have to dig deeper to find how they got the answers, but that is also a part of the learning process, too. If you have access to several editions of the Official Guide to the GMAT, there could be the chance that you will find the answers to some of the questions and problems in the GMATPrep tests.

Greg

Don't take the paper tests anymore...for one thing, they're too old to be relevant. The test has gotten a lot harder since then. For another thing, you really need to be comfortable with the CAT itself, especially the interface.

Definitely do the GMATPrep tests. You can probably find the older PowerPrep CATs, although the interface will be slightly different. But the Princeton Review tests are actually very realistic, and the only non-official ones I bothered using, and they were great. Very useful prep.

Thanks guys, I'll definitely be looking more into the Manhattan GMAT tests for more practice. I have the official prep book (the orange one) and I took a prep course at UCLA that was a pretty intensive review of everything that is on the GMAT, that was the official text book for the class.