I used to use StumbeUpon a lot back when it was popular. Sadly it doesn't exist anymore, as it was bought out and was changed to Mix, which is essentially what StumbeUpon was. I haven't checked it out yet, but it looks similar to what StumbeUpon did. It looks like Mix is a popular service too, might be worth checking it out. But is there anything else like Mix/StumbleUpon?