Though not the greatest place for ambience, La Sirenita is the best place to go for authentic Mexican food in Portland. Always fresh, and with quality ingredients considering it is dirt cheap, Sirenita is almost always packed with the Alberta Street crowd during the lunch hour.
Favorite Dish: The enchiladas are colossal beasts, covered in cheese and sour cream. The fajita platters are also great, and the tacos and burritos are superb.
In a city that's a bit lacking in late-night eating spots, you'll ignore the bad 80s music and neon lights and be grateful for the Roxy anyway. A retro sandwich-and-fries-type diner, you'll probably have a good time here if you like greasy food. Sometimes there's some raunchy stuff pasted on the walls, so don't bring the kids -- or your parents.
On any given weekday you can find a half-dozen street vendors set up along the South Park Blocks, hoping to feed the thousands of students from surrounding Portland State University. They all smell REALLY good on an empty stomach. There's also a farmer's market here on weekends during the warmer months, I think, and another one on Wednesdays in the North Park Blocks.
If you're looking for pizza places near campus, let me suggest a couple. Hot Lips on 6th Ave is always a good pick -- their pizzas are full of yummy locally-grown meats and vegetables and service is excellent. Just a little bit more expensive and less socially-conscious is Pizzacato Gourmet Pizza; they usually have some interesting exotic flavors and the breadsticks are delicious.
Finally, if you like teriyaki and rice bowls, there are a couple decent places around... I just can't remember their names right now.
Taco Del Mar is a Seattle/Portland chain that's basically like Subway, except burritos instead of healthy sandwiches and a fish with a Zapata mustache for a mascot instead of Jered. You stand in front of the counter and tell them all the ingredients you want, and they heap it all together in one huge burrito.
Favorite Dish: Wait until you're starving from a meager breakfast and a long day, then shell out $5.25 for the Super Burrito. That's all I ever get there. They have tacos and stuff too, but they aren't nearly as impressive.
Near Portland State University there are a variety of cheap places to eat, right on campus there are outdoor food stalls that serve middle eastern and mexican food.
On 6th avenue and Broadway, next to campus there is a Vietnamese, Thai, Indian, American pizza place, cafe with teriyaki, etc. Along with the normal chains, McD, etc.
I will write more about this later but wanted to get the PIX online. Worth going to, we had blue corn pancakes and corned beef hash. Both were YUMMY!
There always seems to be a line outside the door of Voodoo Donuts on 3rd Street in downtown Portland.
I swear I saw at least 3 Subway Sandwhich restaurants downtown. This is the one I could see from my hotel window. I did eat a sandwich there for lunch one day.