Some of the tag pages of del.icio.us ranks pretty well for that phrase. Find such pages for your niche and submit your site in those niches. Again don’t spam or try to play with del.icio.us.
Talking about social bookmarking, if you have a funny site, www.fark.com can give you tons of traffic, similarly if you have a programming site, www.dzone.com can give you lot of traffic. If you have tech site, www.digg.com can give you good traffic if the article is good enough.
You can check my list (again few months old) for social Bookmarking websites - http://social.nbridges.com/
Edit - Also look at www.propeller.com as well.