Django
Django is a high-level Python Web framework that encourages rapid development and clean, pragmatic design.
Of course people everywhere compare it to ruby on rails already. Looks a little rougher around the edges right now, but as they say on their download page, django is “not officially launched just yet”. Simon Willison adds a little background.
While i’m on the topic of rapid development web frameworks let me toss in a link to the second rails demo video for good measure. It’s just as impressive as the first one.