Niko Niko's on Montrose is the best greek food I've ever had. I've been looking for something that compares for years, really.
The Original Carraba's on Kirby and Nino's and Vincent's (sister restaurants) on Allen are delicious italian food.
For gourmet food, go for Benjy's in the village or Tiny Boxwood's on West Alabama. Clean and highly tasty paninis, salads, teas, and pastas.
Any of the numerous Mexican joints. TexMex is the only way to go. Goode & Co. Taqueria, Molina's of Mexico City, Cafe Adobe, Escalante's, Mission Burrito, Felix's, anything will serve you well, really.