Please Read and help me ... (niche problem)

I am registered in a CPA network and i always see guys making hundreds off SEO
My problem is that im lack of ideas now

I dont want really to promote direct offers, instead i want to promote the leads through Content and URL lockers.

My problem is that i really dont understand what niche i could try. All i know about are free dwonloads of movies, games and ebooks. Sincerly i cant come with other ideas. Its either i have lack of experience in CPA , either idk what .. (
I have actually a lot of ideas, but i need niches for SEO , that would have thousand of seaches per month on Google and would be demanded by people.

So if somebody got a solution for my problem please help me, or at least tell me how i should search those niches by myself.
Thank you in advance

you could try this
http://www.wordstream.com/keyword-niche-finder

Have you tried using the Google Keyword Tool to get some ideas on how many people search on the niche that you have in mind?