I don’t really use Gmail’s web interface, but if I did I’d download all ten of these apps and plugins and make my Gmail experience that much better. I think the best one on this list is Gmail This bookmarklet which allows you to send blog postings and other things just by clicking a button.
Most of the tools are for Firefox only, but a few are cross-platform.
Top 10 Unofficial Gmail Apps and Add-ons [Lifehacker]