I've found a way to add links to StumbleUpon, Digg and del.icio.us etc on individual blog posts on blogger Quite a nice feature to have. More info and the code is in my sig link
I use a site with one button that sumbits to 10 social bookmark sites. I have to look up the name again.
bookmarking icons and links is not a big deal for blogger.com blogs as template editing is allowed but in wordpress.com either we use a single button AddThis of AddThis.Com or some other manual tricks or a grease monkey plugin that i developed...(very less no. of people use this firefox grease monkey extension but is the most easiest way and wants that you write custom post slug each time you make a post in wordpress.com) If u use wordpress.com check it here http://userscripts.org/scripts/show/10539 wordpress.com does not allow javascript and template editing..so ...
you can use http://www.addthis.com/ which provides you one button and submit to 30 bookmarking sites.