MailBrowser is incredible! Watchout DropBox, this takes the whole sync and collaboration on attached documents to a new level.
Also:
gCalendar ext
gMail Checker Plus
MailBrowser ext
GleeBox
Google Quick Scroll (shows search results on page)
IE Tab for Chrome (renders IE specific Web Pages in Chrome)
Docs PDF/PowerPoint Viewer (no waiting for Adobe or PowerPoint Reader)
Forecastfox Weather
Fastest Chrome: research aid for wikipedia and google search
Apture Highlights: better research than Fastest Chrome