I pick niche first and then look through click bank for product... Any gravity above 100 is good although most of the time i go for top gravity products... I go for SEO model so i don't bother about ad costs...
Twitter is good thing lol Just yesterday some one twitted one of my url on his/her own and suddenly in 1 hour i received 1 around 1500 uniques... I was not promoting any offer but only adsense was on that site and it made me good money... So i think 45k twitter user is good option.... LOL blast them...