After this week's public launch of Su.pr, l.pr URL shortener has been launched and guess what — this is probably the shortest URL shortener. l.pr is the short form of LinksPreadeR (i.e. Link Spreader). Unlike most URL shorteners, l.pr offers a unique feature — you can add comments to your shortened URLs. That is, your shortened URL may look like l.pr/s4/here_is_your_comment.
l.pr also offers a bookmarklet clicking which you can create shortened URLs — something most URL shorteners offer (See also: is.gd bookmarklet).