Go onto a forum specific to game development for much better ideas. There is a forum for software called game maker, you may find some semi-simple ideas there (and a lot of MMORPGs). Then there's gamedev.net, there you can perhaps find more thought through ideas, as well as a ton of MMORPGs.
You insist on getting ideas from us though:
I find that games I play the most are the simple ones such as Elastomania (I lost my profile last year, a profile I'd had for 3+ years), Soldat and Minebombers. Besides that I play some more popular games like the Splinter Cell series (/me shakes head at last one) and of course I can not wait for Fallout 3.
Considering the input you can get from people on a site like this I would suggest a hacking type game. The problem is this has been done before and never well. These games get very repetitive and are very unrealistic.
I can't really think up much else.
Don't forget our IRC: irc://irc.irchighway.net/#slackers
-
WhiteAcid - your friendly, very lazy, web developer