I don't know if I can top Entanglement, yesterday's LunchTimeWaster, but I can try. Or at the very least try to try with Mooo! Mooo! is a physics based puzzler that feels deliciously weighty. It also involves milking cows.
It's simple, and has your typical flash aesthetic, but it's one of those games you'd be happy to play for 10 minutes and then completely forget about. It's easily as fun as, say Angry Birds, and everyone in the universe has fallen in love with that glorified flash game!