I scanned the 170 or so questions from the back of the DM manual, ocr'd them and printed them out some 'cards' (I say cards, but just think paper!) - 8 questions per A4/Letter sheet and cut them out, then on the back I wrote down the answer, this helped in two ways:
1. You have to rewrite the stuff/answers from the books on the back of the cards, so it lodges some of it in your head while your writing it out - This worked wonders while I did nitrox
2. You now have cards, which you can pick at random (or get someone to pick) and try and answer the questions.
I have the questions in Word/Excel etc if you want a copy (Not sure on the copyright here, but I presume if you own the DM manual, then you must be allowed to scan/copy a part of it for revision?)