I am going thru the same problem, I took the test two days ago and scored 500
after going thru most of the OG11
and some Kaplan
At this point I will simply start going over the basic concepts, and rebuilt my foundation. I ordered the Manhattan GMAT
prep series for that.
For exercises, I suggest you turn to the challenges on this site, if you haven't already taken them. But you can always go back to the OG series, with over 300 exercises on each book, it is pretty hard to memorize them all, an any book you get will basically test the same principles.
Good luck to us!