In another acquisition today (see also last.fm’s acquisition by CBS), eBay has purchased website discovery tool StumbleUpon for approximately $75 million.

StumbleUpon offers a browser toolbar allowing users to submit sites they want, and discover new sites suiting their interests by clicking the “Stumble” button, and giving the option to indicate whether they liked the site or not.

Michael Buhr, eBay’s senior director, says:

“StumbleUpon is a great fit within our goal of pioneering new communities based on commerce and sustained by trust.  StumbleUpon’s downloadable toolbar provides an engaging and unique experience to its users, but it is the similarities in our approaches to the concept of community that make it such a compelling addition to eBay.”

At last count, StumbleUpon had about 2.3 million members, and buzz about the site had spread largely by word of mouth.