Chris Madrid's is a San Antonio institution. It's been around since 1977. You stand in line to order, and I've heard that the line is long during peak hours. The menu is small, because they know what sells.
I had the Cheddar Cheezy. It is not a misnomer, people. Be forewarned.
I wouldn't say it's the best burger I've ever had, as there are several Houston contenders, but it was delicious.