Mayhem.cbssports

Simply the best place to manage your NCAA tournament brackets. The interface has improved greatly over the past few years, making it easier now than ever to fill in and track your picks. When filling out your bracket, the site allows you to pre-populate your choices with expert picks, public consensus picks, or any of your previously completed brackets. It literally takes about 5 seconds and two clicks to get a respectable bracket up and running.

Beyond these features, I've found this site to have the quickest updates, best standings board, most customizable options for managers, and overall the cleanest interface. Highly recommended for a site you'll be glued to everyday for the last three weeks of march.