Well anything to do with jobs or finance can make you money but they are generally very hard to rank for. One of the things I do is visit sites like Yahoo answers and Ebay Pulse to see what questions people are asking and what products may be hot yet still evergreen.
For me it is easier to just write about whatever is on my mind. Sometimes I see something on the news and just get an idea. Then once I find something that seems to do well I write additional articles on the topic.