These are some of the sites that I can't resist visiting at least once a day, and probably a lot more. I wouldn't say they are a waste of time... more like a black hole that sucks up every inch of personal time you have, preventing you from ever getting anything done. I hope one day to wean myself off these nightmares.
del.icio.us - Social bookmarking service, shows an endless stream of interesting/unusual urls that I MUST FOLLOW
digg - Community ranked news site, sometimes a lot of crap but usually very up-to-date on the latest news
digglicious - a cruel blend of digg and delicious, uses ajax to display new activity on either site, updated in real time
Arstechnica's gaming forum - occasional good discussion on games. Sometimes I find myself reading some stupid thread for hours.
Google's startpage - Google has a customizable portal page that allows me to view all the latest page feeds. Everytime I glance at it, there's something new and then there goes 15 minutes of my time.
Newsvine - A site offering user-submitted and professional news blended together. Since it's a new site I'm not sure if I'll get sucked in too, but I'm weak so anythings possible.