Thanks samo, for mentioning Niche A Day. I've been subscribed for awhile and its a good service. They don't send you a bunch of ads either. Most times it's just the keyword data.
Keep in mind many of the "niches" they send are not all that nichey and some are really competitive - so mainly use it for idea generation.
Another niche idea stimulator that I like even better because you can gets a bunch of niches right away instead of one a day is the
Random Niche Generator at VREToolbar.
Click "get another niche" and keep doing it until you hit on something that sounds interesting
then CLICK KEYWORD RESEARCH & WAIT A SEC. Some KW searches take awhile. Pretty darned good data for a free tool!