My information might be a bit out of date, since I haven't lived in Tuscaloosa for a couple of years now, and don't do much eating-out when in town for ballgames, but . . .
As kayakerjess mentioned, Pepitos is tops in T-town for Mexican food. With school starting, the one on the Strip may be a bit crowded, but the one across the river on McFarland is just as good.
As far as subs go, Firehouse is a good choice, though it is a chain. I recommend the New York Steamer (full size, of course). Non-chain = Tuts is the best, especially for gyros, calzone and pizza.
If you're down on the Strip and need something relatively quick and filling, give Qdoba a whirl. It's deli-type place (think Subway, but serving Tex-Mex, semi-Southwestern style food), and the quality is somewhere in between Toxic Hell and "real" Mexican food. The Steak Queso Burrito is the size of a Nerf football and particularly decadent. Added bonus: Qdoba is right next to Cold Stone Creamery . . .
As far as burgers, if you're not in the mood for chain restaurants, Buddy's Rib & Steak in Northport is one of my favorite grease pit, hole-in-the-wall type places. Buddy ought to hand out coupons for free angioplasty with every fourth meal or so. Surprisingly, Steve's Grill & Billiards also makes an extremely tasty burger. Don't be fooled by the lack of ambiance at either place. City Cafe, while not open on the weekend, makes a mean burger. I went there for lunch once and got the double cheeseburger plate (obviously, a double cheeseburger with fries, PLUS four veggies). It's not even on the menu - you have to ask for it special - but it was SO worth it. My buddies had to roll me outta there.
Skip the subs and the Mexican food, anyhow. Tuscaloosa is a BBQ kind of town. No need to mention the legendary Archibald's and Dreamland, though allow me to rant for a second: I hate the fact that Dreamland has "sold out" by opening multiple locations, serving pulled pork (and even CHICKEN!), and offering SIDES (other than unlimited stacks of white bread). Times change, I guess. Anyhow, Mike & Ed's is excellent. Try the Brunswick Stew. Bottomfeeders over in old Northport is also good. Foxfire (in the Taylorville area south of town on Hwy. 69) used to be my favorite, but something changed - right about the time I walked in to see a couple of teenagers fixing up the BBQ. Coincidence? I think not. I only went to Woodrow's downtown once, and I won't go back. Admittedly, that was right after they opened, and things might have improved since then, but the customer service was bad, and the food was slow, mediocre and expensive (for what you get).
RTR!