There's too many affiliate products out there for a general question like this... Can you be a bit more specific and least tell us approximately what you're looking for?
Here are some ideas at Clickbank: http://cbengine.com/res/clickbank_cats.cfm If you want to promote physical products you might want to check out CJ.com or Linkshare.com For a bigger list of affiliate networks see my post in this thread: http://forums.digitalpoint.com/showthread.php?t=1277671
As Zaccaria said , can you be more specific on your niche? Thare are lot too many niches , for this general questions. And of course if you want to leanr more about affiliates..etc you can go here , because tommorow i am goona explain how to start promoting products , what products etc. It s a free course about internet marketing.
Firstly check the product. The best performing affiliates actually use their sponsor's products and know them well. Know the market that will need these products and how to create a need for them. Be sure the company is offering a decent percentage commission. Be sure they offer good, quick customer support. Be sure that the company has a convenient method of paying your commission.
Find a niche first and then find an appropriate product. It will serve you better if you understand a niche and exactly what they want and align them with the product. Simply going to clickbank finding out what is selling and working backwards will make it more difficult. Do not base your decision to market an affiliate product on what is the highest selling product(s), find a hungry, desperate niche and connect both with the product, you will notice your conversions will increase and competition won't be as fierce. Point I am trying to make is Research, research and research some more, it will make the next steps a lot easier and yield better results with less tears. Finding the niche is more difficult than going to clickbank and finding a successful, well received product in your market.
I totally agree with Peaker. You need to research the niche and the last thing you do is find the product to promote. This means you wont waste time setting up the promotion that isn't going to make you alot/or any cash.