I echo Paul--
Powerprep 1
Workbooks from Kaplan and PR
Tests from Kaplan and PR
Powerprep 2
OG
Paper tests (If you can get your hands on the genuine article)
This approach has the benefit of showing how much improvement is attributable to the PR and Kaplan stuff.
Many times it has been said that you ought to mark every question you miss, catalog them, and go back and do each of them again. I wish I would have started this earlier.
Rinse, lather, repeat.