In case somebody out there is thinking about doing DLM's 7 circles using books, I offer up my first group of 40 exercises as a starter. They are from the following books:

1. Seirawan's Winning Chess Tactics - great writer and player
2. Burgess' The Mammoth Book of Chess - more towards intermediate and advancing players, a helpful reference
3. Laszlo Polgar's 5334 Problems, Combinations, and Games - fun, large, and bricklike, containing many, many mate problems
   
4. Problems at the end ("Ben's") of my list are from positions I have gathered. Warning! One of the positions is illegal - I use Winboard to open it; it's from Chessmaster 8000's "Move to Safety" drills which has no Kings. Position 4 and 5 are mistakes I would rather not repeat. Ahem.

It's a fairly easy group, but still a challenge to do all in 20 minutes. The Polgar 5334 list covers every major theme for mate in 2, using the most essential examples I could find. Good Luck!