Life long resident of Madison, and Vientiane is hands down the best Thai you'll find in town. Their curry squash dish is absolutely amazing and their pad thai, as cliche a dish it may be, cannot be beat. Don't forget to try the Lao Noodle Kee Mow, it is an AMAZING noodle dish! I'm a meat eater, but their tofu and the way they prepare it is a must try!
There are 3 restaurants in town, but the one on Park St., while superior in atmosphere, lacks in recipe for some reason. The Gorham and Regent locations are amazing. Don't expect much for service from the Gorham location, but rather the best Thai you'll find in Madison.