There is a mile-long stretch of Western Ave that contains many delicious Thai Restaurants, including the aforementioned Spoon and Opart, which are right near the Western Brown Line stop. I'll also throw in Sticky Rice, which of course has excellent sticky rice. It's a little less than a mile south of there.

I'll second Arturo's for Mexican food, although that is partly because I eat there all the time since I live near it. I'm also partial to Garcia's, which is pretty much right across the street from Opart.

Roseded, 2308 Leland, blows both of those away and they're much cheaper.

Thai = Opart

Mexican = El Asadero (burrito/taco place...corner of lincoln/montrose)
Los Nopales (sit down, really great, little more spendy...@ wilson and western)

this is all north side-ish, but i swear its all awesome!

If you don't mind going a little southwest try this mexican place:

http://www.elfarorestaurant.com/

They have a good vegetarian selection and the best 'tacos de rajas' in town. Won't be disappointed.

If you can handle the wait and the lack of seating, Picante on Division is really good for Mexican. I suggest the Chipotle Chicken burrito.

Opart and Spoon are good, but I agree with camilo about Roseded.

I haven't been to Roseded in years. They were really good, then the quality went down. I'll have to go back there, because I used to love that place.

Dang, yeah, Los Napoles is great too. Such a great stretch of restaurants there on Western.

I'll recommend Puebla on 2658 N. Milwaukee for Mexican. Awesome massive burritos, and the best horchata in the city.

Others on this board will back me up on La Pasadita (1140 N Ashland Ave), which I've mentioned before. Great cheapie tacos.

For Thai, I'm a fan of Charley Thai on 3209 W. Armitage. I plan on sampling everything on the Menu, since its all so good. If you plan on actually going, the dine-in isn't open until after 5.

P S Bangkok Restaurant on 3345 N Clark St. is also quite astounding.