I doubt many people are going to share their high earning site ideas with you. The last thing I need is another competator
content related sites. Blogs do well if you are unique and have traffic. Stay away from forums and community stuff unless you have loads of traffic.
Fora forum it depends on the niche largely. One of my automotive sites makes about 900 a month with about 100K uniques a month. I have other sites that make a couple hundred a day with a fractionof the traffic. Too many variables to take into account. Also too many secrets to give away if I delve into the variables too far