I'm a Houston girl born and bred! The original Ninfa's (on Navigation) is spittin' distance from my office, not to mention the one downstairs in the tunnel below my building, and there's one on Westheimer near Wilcrest, just around the corner from Casa de Xena.
I've been to the original Ninfa's years ago. Ninfa's in Waco took an old warehouse building downtown and renovated it -- very nice. Ninfa's has great food, but when I want down and dirty TexMex I usually choose one of the locally owned dives.