Myles' list is the most accurate for greater Houston, although as he pointed out it does have a few errors. The repeater scene in the big city is in a constant state of flux, and the only way to get an accurate handle on what's really going on is to scan every pair in the statewide channel plan.
146.88, 146.92 (Saltgrass), and 146.94 are some of the more active 2-meter repeaters. 440 is a toss-up with a lot of linked systems and AllStar activity. There are a couple of active 220 repeaters with good coverage, too.