TCH is always good, if they'll let you volunteer. I used to frequent the children's ward there, and loved it when the volunteers would take me around and play games and stuff.... Try meals on wheels. You sign up for a route for a day and drive around delivering meals to all sorts of old people around downtown. I used to do it all the time for NHS in high school. Or there's always old folks homes.
Don't forget about the various Superfeasts on Thanksgiving day. If you are not too busy with family on that day, I highly recommend it. It is very fulfilling to feed the homeless and hungry on Thanksgiving day.
I'm just getting started volunteering at Covenant House Texas. It is a shelter for homeless youth. I'll be helping the youth prepare for obtaining their GED as well as going out in the van and recruiting them to come to the shelter and get off the street.
The YMCAs around town always need volunteer coaches & assistants - soccer season starts in a couple of weeks...woooohoooo. I mentioned this in another thread, but check out the Special Olympics, it's probably the most rewarding thing I've ever done.
There's no real organization backing this cause, but what I usually do when I'm feeling charitable in Houston is go to 5th/3rd Ward and buy up all the crack that I can find. Then you take it to Katy/Sugar Land/Kingwood, double the price, and sell it all back to the community. Taking crack from the poor and giving it to the rich. Like a reverse Robin Hood, but since crack is "negative," simple mathematics will yield: (crack)*(reverse robin hood concept)=positive A negative times a negative equals a positive, as Edward James Olmos taught me.
Although I am a volunteer for the Muscular Dystrophy association, I will be running in a 5K on Oct 4.......its for Breast Cancer.....if you would like to run it please email me or click on this link http://www.kintera.org/faf/home/default.asp?ievent=26328&lis=1