Originally Posted by SamWP
If you don't have a topic in mind and your only reason for blogging is to make money then you are setting yourself up for failure.
My suggestion would be to blog about your passion. Whatever that maybe. Do a little research on it and see if it is something that gets decent search traffic.
I wholeheartedly agree with this. The search engines have gotten quite keen on those people who start websites or blogs with monetary motives. The bar has been raised substantially so that the most knowledgeable, informative, entertaining, etc., pages rank the highest.
Competition on the Net is quite fierce these days.
You really have to know your stuff. So a better question to ask is, what topics do I love, or what do I know a lot about?
That's why you should go with something you have a passion for and/or a decent depth of knowledge about. Then be prepared to work hard. Also, get creative to find ways to make your passion earn. New, unique ideas are very valuable these days.