I recently begin learning Python web frameworks (I'm not a big fan of Ruby's execution speed) and did a bit of googling on them. Of the three most popular ones, namely Django, Turbogears, and Pylons, Django is by far the most popular of the three. According to both the wealth of information and google trends, Django is magnitudes more popular than the other two (yes, I know google trends doesn't filter out non web framework related results, but I believe it's still helpful). And it is easy to see why. Django has the best documentation, debugging information, and 3rd party help guides to help you get started. It's even got a second book coming out later this year and it's online now in form of a beta release.
After trying it out for a few days, I recommend Django for those who are new to web development. This is a recommendation only for newbies since I'm new to this myself. If you've been working with Django for a while, you may find it a bit "closed" according to many people. In fact, it is because of Django's reputation's of being a closed and non-flexible environment that I started learning Pylons first. (I did not look at Turbogears as much as all the information point out that the idea behind these two frameworks are very similar -- utilize the best of the other web framework components out there. Turbogears is said to be more mature and better documentation Pylons, but is in a flux of a major 2.0 change. Maybe I'll give it a try if Django doesn't work out.) Pylons seems to have only a tutorial, a cookbook, and a 3rd party Quick Site Guide. And that's it! There's not much more out there. So after spending three days on it, finding myself getting stuck more often than I like, and see no where I can go to expand my learning experience, I went over to Django and am glad I did!
References on my decision making:
Python web development and frameworks in 2007
Django and NIH
Python Web frameworks, Part 2 (scroll down to Conclusion)
TurboGears and Pylons (a technical comparison)
(There's many others, but as the title says, this is suppose to be a time saver for you, so I leave out the not too important ones)
web.py - "the anti-framework framework"Reddit uses it.