The best brewery tours in town are at the brew pubs. Check out Minneapolis Town Hall Brewing for tours the first Saturday of every month. Free pint before tour, tasting glass, samples on the tour, 10% off food - cost $7.
Although I have never been on them, Flat Earth and Lift Bridge (next year) offer tours.
I haven't been to Lift Bridge yet but I was not impressed with the Flat Earth tour. It was very basic, tough to get questions in, and good luck getting answers to follow-up questions via email afterwards. The beer is OK though. I agree that Surly is the tour to take but like everyone says, good luck signing up.
I know that the weekend tours require reservations, but has anyone had any luck getting one of the weekday tours on short notice?
I've been to Summit once for a tour, and it was a weekday, and I had no problems getting in, I'd say just get there a bit early. This was during the summer as well, I suspect that during the winter it would be even easier.
I would like to go again, because they didn't have any special brews to try while I was down there, and I would like to catch them when they have something interesting in.
I recommend also checking out the Flat Earth Brewery. It's not at all on the same scale, but is the kind of brewery most homebrewers could actually consider starting if we had the determination.
Flat Earth is also in the same industrial area as the Summit Brewery, I haven't checked the schedules but you could conceivably get in two tours in one day!!! There isn't much of a "tour" in that you pretty much see the entire brewery when you walk in. It's mostly Jeff (owner/brewer) telling you about how he got into the business and fielding questions. There's also a generous availability of samples and you can buy growlers. They've got fantastic beer, love the Angry Planet Pale Ale and Northwest Passage IPA.
Going to have to second the suggestion to visit Flat Earth.
It's easier seeing myself starting up a brewery like Jeff's more so than what Omar has done over at Surly. Most of us don't have a family with spare space in a giant warehouse to start a brewing company. Omar tells a great story (it's gotten LONGER at each subsequent tour) and Todd Haug has created some fantastic beers for Surly. I've gone on the tour several times and there is always something new as Surly's been constantly expanding since day one. But as it's already been said, the tours are hard to get into.
You don't even need to do the tour at Flat Earth. You could just show up any afternoon they are selling growlers and most everyone is around to chat about the brewery and you can sample to your hearts content. Love their NW Passage.