I use flv video downloader in firefox. It's a little more low level than most tools, it actually detects the flv being streamed into the browser, it's not parsing the html source to get at the file. Works on xhamster and most any other site I've tried it on. Can get a little confusing, though, if there are ads being played before the video or what not, so pay attention to the file sizes.
Also, to play the flv files, use VLC media player. Plays most any type of video file. http://www.thestuffcenter.com/flvmoviesdownloader