Unexploited niches are treasures, but unexploited markets are treasure islands. Sometimes general keywords/niches can be used for your SEO and Adsense. You know the biggest potential in terms of niches and markets? I think it's Google China. Those countries that don't know much about SEO are big markets in my opinion. I know one fact that they sell PR6 link $100/mo. The craziest thing is that their SEO knowledge is so small that they even buy links on expired domains.
fav niche or high paying keyword niche uR Title shows u r asking about other ppl fav niche but details shows u r looking for high paying ads. finance, calling cards, VOIP, loans, business, credit cards, domain name, hosting, life insurance r some high paying niche