flippa
buysellwebsite
websitebroker
webhostingtalk
digitalpoint
geekvillage
webmaster-talk
dnforum
craigslist
ebay
loot
Thats just a starter.
I could go on all day.
It does depend on how much traffic you get, what site earns etc etc as to where the best place to sell it would be.
That is something you will know when you look at the sites above & other similar sites. If something similar is on the market or has recently finished & fetched an ok price then that would be a good place to try.
Most forums have a buy/sell section also. So a forum that you participate at might be ok too.