Hmm. I have had thousands of game ideas in the past. Most of them were horribly similar to games that already existed, depending on my state of obsession. I once drew this DKC/BK ripoff starring a lizard, and I was the final boss ('cause, you know, it was my game idea). Later on I made a Zelda-type game starring the boss version of me. I even made a Kirby ripoff about a little round alien with really strong antennae.
As for the present, (read: not in the past) I have been pondering for the longest time an original game idea. The best I could come up with is a game that combines elements from all the major genres: Platformer, Adventure, Racing, Fighting, Shooting, Puzzle, Strategy. It would have it all. Though it would probably take a while before games that big can be made.