Below you can find a list of the most used ones, simply replace "[URL]" with the URL to your site or specific page and "[TITLE]" with the title of it. Some services have additional parameters, but they are pretty self-explanatory.
Note that you always need to urlencode your URL and title!
Del.icio.us:
http://del.icio.us/post?url=[URL]&title=[TITLE] Furl:
http://www.furl.net/storeIt.jsp?u=[URL]&t=[TITLE]
Digg:
http://digg.com/submit?phase=2&url=[URL]&title=[TITLE].
Google Bookmarks:
http://google.com/bookmarks/mark?op=edit&bkmk=[URL]&title=[TITLE]
YAHOO MyWeb:
http://myweb2.search.yahoo.com/myresults/bookmarklet?u=[URL]&=[TITLE]
BlinkList:
http://www.blinklist.com/index.php?Action=Blink/addblink.php&Description=[DESCRIPTION]&Url=[URL]&Title=[TITLE]