Gmail Labs now let you add gadgets to the left-nav, next to Chat and Labels: “a simple way to see your Google Calendar agenda and get an alert when you have a meeting, and a gadget that shows a list of your recently accessed Google Docs and lets you search across all of your documents right from within Gmail”. In addition, there’s also an experimental features that allows you to add any gadget by pasting in the URL of its XML spec file e.g. http://www.google.com/ig/modules/youtube_videos.xml.

To make room for the gadgets, you could try these experimental features from Gmail Labs: Right-side chat, Right-side labels (move Gmail Chat and the list of labels in a right sidebar) and Navbar drag and drop (reorder containers).