There is no end of profitable niches online & there are many of them that seem to do very well for paid search marketing. You want to pick such niches because you can get traffic fast, test fast & profit fast.
AdWare & SpyWare
Personally, I am not into this, however, I know people who are making a lot of money in this market. Many of them put up review sites then they bid on the name of almost every computer or internet related virus. For this niche, you can promote different ClickBank products as an affiliate. The search volume is high, so is the competition, it is a clear indicator of a profitable niche.
Vehicle Auction
This is a very interesting market which I did not know about until a friend of mine told me about it. You can put up a presell page then bid on all the names & models of cars which have high searches. This niche has lots of keywords, lots of opportunities. There are enough ClickBank products you can promote as an affiliate. If you want, you can even compile your own listing of vehicle auctions & sell that listing as a downloadable report.
Public Records
This is another niche which I never knew till I was told about it. When people want to do reverse phone search or they want to check the background of some company or individual, they search online. There are a few ClickBank products you can promote as an affiliate. This is another good niche with lots of long tail keywords, lots of hidden opportunities for profits.
Summary
These 3 niches have been around for awhile & because they are evergreen, you can build your business around them. They all have ClickBank affiliate programs which you can promote & they all have lots of keywords you can test.