Reddit is not a bad source of backlinks, but i think best sites are digg & stumbleupon. Try these sites, your ranking must be improved.
Reddit I've had great experience with traffic. Also, SU - both are great SBM sites. I don't think that either one are doFollow though.
Digg is no longer a good place to build links as it's nofollow. There are lists with over 100 dofollow social bookmarking sites and their PR. I'd suggest getting a list and then picking some of the better ones and submitting your articles to these daily.
It is a good idea to use many diffrent social bookmarking websites. If you need some resources here is the list which I use http://marketing-a-website.blogspot.com/2009/05/top-55-social-bookmarking-websites.html