Here are two interesting plugins found after upgrading wordpress:

Plugin Central (compatible up to 2.5)

A byproduct of the native automatic updating in Wordpress 2.5, features includes mass plugin update, install from URL, and mass export to another blog.

Ajax Comments-Reply (compatible up to 2.5)

This essentially replaces the Quoter, Threshold, and Ajax Comment plugins. If the author adds threaded (collapsible) comment support and comment rating, this would be a five star plugin.