I'd have to say that any steel frame bike that can accomodate fat tires and fenders would be the most practical choice in a commuting frame. Braze-ons are an added bonus. And if you can find a used one that's cheaper than new, that'll make your bike even more practical.

I'm currently using the Surly LHT--I'm pleased with how inexpensive the frame was and how well it rides with all of my components. I've got a flat bar setup, randonneur box/bag up front and a rack w/panniers in the back. There are lights all over the bike and it's still under 30 pounds.