Of course, Fort Worth is known for it's Tex-Mex food!  One of the local favorites is La Playa Maya--they specialize in integrating seafood into traditional Tex-Mex dishes.

Hot Damn Tamales is also well-known for its interesting varieties of this Mexican fare.

If you're looking for upscale, modern Mexican, try Lanny's Alta Cocina on W 7th.

You can also find local taco vans in parking lots in the evenings in south Fort Worth neighborhoods--very cheap Mexican food that local Hispanics line up for, but you'll have to take your chances on quality and cleanliness.