If I am considering working in a new niche, I first do a Google Adwords search to find terms that people use to look up information. When I find something of interest, I then use a program called Market Samurai for doing detailed keyword analysis and for assessment of potential competition for my selected keywords.
I strongly suggest using Market Samurai for these detailed analyses and finding profitable niches. The program uses data from Google for keyword analysis and from Yahoo for site rankings.
The program uses what are called the "Golden Rules", which is the default format for preliminary analyses. One of these rules is to have 50 or more hits per day for a keyword. This helps find the overall category that you can use to create a domain that has market potential. These settings can be changed to help find topics for pages or blogs that are related as well.
So, if you are serious about what you do on the internet and you want lots of people to notice you, this is an option that you shouldn't overlook. I can help you get off to the right start and provide guidance for future work that you do on your site to help build traffic.