I started out with ParkNFly in New Orleans and discovered they are also at IAH so I have used the same cards.
There is a free day coupon here. They also give AAA discount.
http://www.flyertalk.com/forum/Forum...ML/009277.html
At Hobby I have started to use Sunpark. There is an ENT coupon for them as well as a discount for Southwest RR members (20% I think) I also recently bought a book of 5 days of pre-paid parking from them for approx $25.00. They had a deal going where buy 1 travel pack get 1 free. That means I got 10 days of parking for $25.00. I'll be using it next week so I'll report back if there is any downside.