Probably my favorite Starbucks in Madison. It can get busy at times, but there's generally seats available, and there are enough outlets around to be able to find one. The baristas generally turn drinks around pretty fast, and I feel much more welcomed here than I do at the State Street location. Plus, the windows here are big enough to let a lot of light in and enjoy the Capital view. Those along with the outdoor seating are perfect if you want to people watch for an hour or two. The biggest downside is probably that there are generally your typical Madison protestors, paper pushers, and whatever else standing out right in front.
It's a bit of a walk, but anything outside the capital square for the most part is free 2 hour parking if you come during the day and don't want to pay for a parking spot.