I'm a big fan of long form improv and find the troupes at the Torch Theatre never disappoint. My favorite shows to attend are the Neighborhood and Cage Match. At the Neighborhood, the Torch invites a local to come and tell stories from their life. The troupes than perform improv based on the stories. I've discovered some awesome local poets, musicians and writers from these shows.
Cage Match is a competition between two troupes. Since it's later in the evening, these performances can get a little raunchy, but I've found the improv artists are more apt to provide more clever and smart humor.