I updated Randtastic (shiwej.com/randtastic/) so that it passes each random URL back to itself. This enables you to go back, and also solves the issue of sites breaking out of the frame.

There has also been a browser shortcut for a while (ALT + r or Ctrl + r) that enables you to quickly get random pages. The site also filters out adult content by default.

I've been using this myself all the time, and have found some gems now-and-again.