Houston's a good theater town. Try a play at the Alley, TUTS, Stages, Ensemble, Main Street, etc. The UH School of Theater has professional-calibre shows for the price of a movie. Dinner and magic shows at Magic Island. Various Comedy Clubs (try Comedy Sportz for great improv). Radio Music Theater does great comedy sketches.

The Miller Outdoor Theater has something showing 3-4 nights a week, from May through October. Various types of music, Shakespeare, full-scale musicals, symphony, etc. It's always free.