StumbleUpon is rumored to be in talks of an acquisition with eBay.  According to both GigaOm and TechCrunch, Google and AOL are other potential suitors as well.  The amount is rumored to be $40-45 million. 

Stumble Upon has a toolbar where users can rate various websites.  StumbleUpon badges appear are seen on blogs and other websites including Pulse 2.0 at the bottom of every post.  Essentially it is a website recommendation system.

StumbleUpon has 2.1 million users and has raised a previous $1.5 million in funding.