There are lot of bars when you can get a good to excellent beer selection. These are the ones that stand above the crowd in a town that knows its beer pretty well. This list is in approx order.
Nick Lyons: 25 or so taps, the selection is American and very rare, and stretches from coast to coast. The taps change quick here. Draft Magazine top 100 bar.
Nick Lyons: Great Belgian line-up, lots of beers in bottle and 30 or so on draft. Sister restaurants Cafe Central and the Hollander in the East side have good, but slightly smaller, beer menus typically.
Nick Lyons: Not known as a beer bar, but it's draft and bottle list are worthy of it. Excellent offerings with the bonus of actually feeling like a local bar and not a 'beer bar', if you're not into that.
Nick Lyons: A borderline on this list, but they've been doing a lot of work with less taps lately. Sophisticated offerings for a place that wasn't always known for this much good beer.
Nick Lyons: Consistently the best service and variety for German beers, a category often forgotten in a town known for its German heritage. All the great wonderful German classics are on draft here.