Even though this is a stupid question, I'll answer it seriously...
I find so many profitable niches by looking at ads in newspapers, billboards, signs on bus stops, taxis, etc, magazines, radio, tv, etc...
Profitable niches are EVERYWHERE you look. You just need to pick up on it correctly.
Great answers but I think he's really asking how to find profitable niches that aren't oversaturated and where someone new can get in and compete.
I mean, every niche in the world is profitable. Just not for everyone.
Lots of great ones already given, I'll add a couple more.
Infomercials. The ones that run many times each night and have been running for a while, they must be making money. If you see a new infomercial, hurry up and get a site up for that niche because there are going to be a lot of searches for that product/niche
I've gotten some of my best ideas from my friends and family. None of them have any computer knowlege and are far from internet/computer savvy, when they get online they are usually looking for very specific info. Knowing how they use the web and how they search for the info has given me a shitload of nice, profitable niches, many have little or no competition and you can rank like a mofo.
Infomercials. The ones that run many times each night and have been running for a while, they must be making money. If you see a new infomercial, hurry up and get a site up for that niche because there are going to be a lot of searches for that product/niche
Hows that antique used douchebag niche working for ya?