Not really a "site", but IMO usenet is by far and away the best source of porn on the internet, especially if you are willing to shell out about $10/mo or so for a premium usenet provider (most ISP news providers are crap and have short retention times). Even if you aren't willing to pay any extra, you can still get some good stuff with the freebie news server your ISP most likely provides.
The learning curve for usenet can be a bit steep if you've never done it before though. Fortunately, there is help available -- go to
the alt.binaries.multimedia.erotica FAQ to learn all you need to know, including what software you need to get started (don't worry, pretty much everything you need is free).
Another tip is a site I came across that indexes usenet posts and provides picture previews, even for posts that didn't include previews originally. The site is
UsenetBinaries.com. The deal is that they are trying to get you to sign up for their pay service, where they decode all the binaries for you and you download directly from their site (a pay service). However, you can sign up for their free trial account (no credit card or anything needed) and have unlimited access to all the previews. It's great -- I go there to see what I want to download, then fire up my newsreader to go get it. It's also handy to get suggestions about what groups to download from -- there's *way* more out there than just what's in alt.binaries.multimedia.erotica.
I'd be happy to answer any questions about getting started downloading from usenet if anyone wants to pm me.
As for actual web sites...adultbouncer is good, though you have to find the sites that update frequently, and it gets old going to site after site that all have essentially the same content. CDgirls is pretty hot, but maybe that's just beause I really like Sybian videos.