one option is to become a Jr. Vip and post it here. If it's good domain and the price is right you will sell it, I just don't know how fast it will be...
Another option (and probably faster) would be to sell it on Flippa, but I think you'll incur monthly charges for having it listed there, plus a 15% deduction from the sale price that Flippa takes as commission. Or it might be 20%, I've forgotten the rates but they used to be high anyway....
Also, I've heard people say that Facebook groups are a good place to sell domains and sites, but how to find the right group for this I have no idea, so you'll have to do research on this...
Last but not least, PPC is always the fastest way to sell things, but you'll probably spend a lot of $$$ upfront before someone buys it. But if you're good with the salesletter and offer a decent price there's - sadly - no bigger exposure for your ads than the one from google, so you can try with that too...