I'm not in Chicago right now, but I grew up there, and the ethnic food is incredible, although I'd imagine most people (even current students) are not looking in the right places. Ethnic food in Chicago is great, but it's not that great in Lakeview, Lincoln Park, or Streeterville. I went to college in Claremont, outside of Los Angeles, and even in deeper trips into the LA, I didn't find anything that Chicago couldn't beat.
Chicago actually has incredible Mexican food, and you can get even highly particularized regional Mexican cuisine as well -- you can find places that specialize in Oaxacan food, Yucatecan food, etc. However, if you want the best you'll have to go to the actual Mexican neighborhoods -- the biggest being Pilsen, but there are lots of other ones as well. On the North Side, Lawrence west of Lincoln Square provides some great options.
This is reflective of something you will find overall about Chicago -- it is a city of neighborhoods, often particular ethnic neighborhoods. Rogers Park has the best cheap Indian food in Chicago... and also Pakistani, Lebanese, Israeli, and the only Georgian (as in ex-Soviet Union) and Croatian places I know. If you want Korean, go to Albany Park. There are decent Chinese places all over, but for the best, you'll have to go to Chinatown. Lincoln Square still has some traces of its German heritage. The South Side will have the best soul food.
If you really want to explore Chicago's food scene, I recommend coming with a bike and making the most of September. Lthforum.com is a great Chicago-based restaurant message board, and they put together a great map of places they've awarded the Great Neighborhood Restaurant designation. Check it out: https://maps.google.com/maps/ms?ie=UTF8&hl=en&om=1&msa=0&msid=115707820952343749632.00000111c483d5e1c71db&ll=42.103317,-87.897491&spn=0.680621,1.126099&z=10
Here are award-winners broken out by cuisine if you're looking for something in particular: --LinkRemoved--
For Mexican, this is a good start if you're looking for steak burritos: --LinkRemoved--
And a discussion of Chicago vs. LA Mexican: --LinkRemoved--
Believe it or not, I am not even fat -- just mentally.