Bombastic is gonna be a sequel to Devil Dice?! Sweet. That was a great puzzle game. I could play it all night, but I could also get non-gamers *cough*my girlfriend*cough* to play it, too.
I second Military Madness, too. There was a summer when I was about 12 that I was away from home and played the hell out of that.
And I've got one to add: Hexxagon. It was a shareware game from way back. I couldn't even remember the name, but this thread made me look it up. AND, I just found a Flash version of it too. Happy happy happy.
http://www.neave.com/webgames/hexxagon/
Edit: woops, wrong url.