To answer that question, it would help to know a couple of things.
1. How quickly are you looking to sell them?
2. Are you looking for end-users (someone wanting to develop the name into a website), or reseller's/domain investors?
Most forums you are going to are only going to fetch reseller prices. Flippa also has a very high amount of resellers. If you are seeking end-users then the best sites to sell on would be Sedo or GoDaddy Auctions in most cases.
It also matters what the domains are and what the extension is.