I personally like http://www.infonary.com. They have a good interface and apt information. You can browse through topics like business, religion etc. This site also provides a search functionality
I will refer to one of my favourite lists of social bookmarking sites which is here http://www.caroline-middlebrook.com/blog/do-follow-social-bookmarking-sites/. The good thing about them is that they are all do-follow and you certainly have an advantage over showing those badges on your site as any bookmark followed will bring a valid inbound link to your site which will be transparent to Google (sites like yahoo disregard the nofollow tag anyway, and the link equity is passed unlike google). Do try them out and you could see from our webmaster tool account that google actually sees it. I've tried this for my video sharing website and it really works.
stumbleupon, del.icio.us, reddit and digg are all worthy a try. To the social bookmarking, everyine independent site has its own emphasis, so find the right thing is the key!