The
"Museum of Modern Betas", a site that is dedicated to keeping track of all those new Web 2.0 apps that are popping up every day, added a great resource to its site:
The hottest betas in the webosphere. The list is based on the number of bookmarks at del.icio.us added within the last 7 days, which is a really interesting parameter. Pretty interesting for everyone who tries to discover successful startups before everyone else does (VCs, journalists,...).