Money Online

The first and most important condition when choosing a niche for your website or blog is to find something that you really know a lot about and love to write about.
However, this is not enough. Before going into writing and designing your site, be sure to check upon to things:
1) How many people are interested in knowing about what you are writing
2) How much competition you have in that specific field.

These points are crucial and you seriously need to take them into consideration before adventuring further. The good thing is that they are very easy to check, and a few minutes can save you a lot of weeks of working in vain.
First thing you have to do is to choose some keywords that you think will drive visitors to your website and go to http://inventory.overture.com/d/searchinventory/suggestion/ and check how many searches where done for those keywords in the past month. If you consider the option of making money through contextual advertising such as adsense, ypn, bidvertiser, etc., you may also want to see how much people are willing to bid on those keywords by going to http://uv.bidtool.overture.com/d/search/tools/bidtool/
If the numbers resulting from the research mentioned above seem ok for you, you are ready proceed to the next step. In order to see how tough the competition is in that niche you must use the seomoz keyword difficulty tool http://www.seomoz.org/tools/kwtool.php and follow their instructions. A report can take some time to be done (usually around 30-40 minutes) so be patient. When you have the results, you can make your decision; if the competition is low, than go for it, but if it goes above 50% than you might consider another niche, since it is becoming more and more difficult to get visible with that kind of competitors, and you will probably have to invest some money to get powerful links to your website.
Good luck!

Technorati: Site promotion, Niche websites