http://www.pligg.com has a list of sites the CMS uses. http://www.jossle.com/ http://www.gamesnips.com/ I guess you can count netscape.com as well.
Ahh I also run a digg style site (for forums) called ThreadSoup.com. Precisely how "popular" are you looking for the site to be?
How about doing a search on DP forums. Long back I have bookmarked this thread. http://forums.digitalpoint.com/showthread.php?t=27977 Check it out.
theres shoutwire.com aswell, but none of these sites are very popular compared to digg. As you can see on shoutwire there are stories on their homepage with only 12 'shouts'.