Most of mine are .com.au or .net.au (e.g., body.net.au, industry.net.au, rating.com.au, lends.com.au, knows.com.au, etc), but I have three .coms I have never got around to using:

twitcorps.com Plan was for a register of businesses using Twitter, categorised by how they were using it and how well they were using it. It would be a way for newcomers to get ideas on how their businesses could give it a crack.

topictwits.com The idea was basically wefollow.com, but then that got released and so I forgot about it.

popslide.com First idea was for people to email a bunch of photos and get back a URL pointing to a quick, thumbnailed gallery. Like what Posterous does, but for one-offs. Second idea was for something similar, but you'd email a sequence of statements and you'd get back a URL pointing to an animated Flash presentation (a la Powerpoint) that you could tweak and style later.