May be of interest to those with multiple accounts who wish to consolidate at some stage. Will be available to all soon: http://schlottke.org/jacob/2007/02/12/add-yahoo-hotmail-and-pop3-e-mail-accounts-to-gmail/
Another good one on the gmail side of things in the CustomizeGoogle plug-in available for FireFox. This allows you to remove ads from Google's searches (each separately - images, froogle, etc), block tracking by Google Analytics, and a lot more.. http://schlottke.org/jacob/2007/02/11/hide-the-gmail-spam-counter/ Some of these things web publishers wont probably like because they want to see the exact display, but if you have a computer you use for personal use only, it is always nice.