Yeah use Flippa.com or you can even post it in the Buy/Sell/Trade section here on DP. There's an area to list sites you're selling.
There isn't really *one* place. If there is, that *one* place consists of many websites, such as flippa, sedo, sitepoint, dp, ebay and tonnes of others. Don't just limit yourself to one site, thats ridiculous.
As sad above probably best to list in a few places, although always state you have listed elsewhere and may be sold at any time, that way you won't have annoyed potential buyers if is suddenly sold elsewhere. Having said that Flippa is probably the most used place these days
@david01130 As long as your site ain't junk you shouldn't have any problems selling it on Flippa. Warriors forum and DP (the marketplace section of the forums) should work as well for sites ranged between $xx,xx - $x,xxx. Al.
definitely Flippa also, if your website does not get enough traffic, you may consider boosting it's traffic rate by sending dirt cheap auto traffic to it to boost its alexa rank and look more appealing for potential buyer
Sitepoint, flippa, DP, Warrior. Those are good sites to sell your site. Maybe you can try sitesell.com.