People spend a lot of time in email applications, so it makes sense to have links to other applications and useful information next to the email. Some would like to see their bookmarks, others would find useful to have their agenda and the list of to-do items.Gmail Labs lets you add two gadgets in the left sidebar: Google Calendar and Google Docs, so you can add events, see your agenda and open recently-edited documents. There's also an experimental feature that lets you add any gadget by entering the address of its XML file, but I couldn't find gadgets that work and look well.
"We realize this isn't very user friendly right now; it's a sandbox mainly aimed at developers who want to play around with gadgets in Gmail. We're not tied to the left-nav as a primary way to extend Gmail -- in fact we think it is relatively limited and doesn't offer scalable real estate. There are also some downsides to the iframe-style Gadgets we're using today -- they can sometimes slow down the page. We're fanatical about speed, so we'll be keeping a close eye on performance," says Dan Pupius.
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).
{ Thanks, roody. }