Here is a simple map I've created to help friends from out of town who are coming to San Francisco:
The Mission district has some pretty good eats; I would recommend checking it out if you don't mind making the trip. It's not terribly far, and there's a number of ways to get there; bus, BART, and even walking, which would probably take around 20-30 minutes. I remember taking the Scandinavians there last year, meaning to go to this vegetarian sushi restaurant but ending up finding this really amazing Falafel place. You really can't lose. They've got everything ranging from Mexican, Pizza, Sushi, Vegetarian, Mediterranean, and much more.
There's some restaurants on Mission Street itself, but I think most of the best ones are on Mission St's parallel, Valencia. You'll probably want to start at 16th and explore down to 21st on Valencia; it's pretty much nothing but amazing food for those five blocks. Anyways, I'm a little biased because I'm vegetarian, but here are some of my favorite spots in the area:
Ali Baba's Cave - This is the Mediterranean place I spoke of, where you can get one of the best Falafel wraps I've ever tasted, with everything in it, over a foot long, and for around $6 USD. They even take credit card. They also have lamb, beef, and chicken options. Highly recommended.
Herbivore - This place might just change your mind about vegetarian & vegan cuisine, omnivores! This place is seriously really good, and even non-vegetarians will enjoy it (I've taken plenty there, and they always do). I recommend getting the Chicken Shwarma Wrap (of course it's not real chicken!) Their prices are usually around $10 - $12 per person.
Cha-Ya Vegetarian Japanese Restaurant - Well this is weird! Rarely do you see this combination, but if you're a vegetarian and really in the mood for sushi, then this place is for you! They make some really good vegetarian rolls and they also have a variety of other things, so check them out if you're vegetarian... You might even like it if you're not
You might spend anywhere from $10 - $20 per person here.
Other than that, there are plenty of other options, but those three are my best recommendations for the Mission!
If you're in the market for something closer to GDC, but in a slightly more "interesting" neighborhood, you might want to check out the following places in the Tenderloin:
Lahore Karahi Indian - This is one of the better Indian restaurants I've eaten at in San Francisco. It's not just for vegetarians, either! Plenty of great dishes to please anything. The only downside (not sure if this still applies; I haven't been there in a while) is that you might be waiting a while for your food.
El Tesoro Taqueria & Grill - This was one of my favorite Mexican Taquerias back when I hung out in this area. I mean, I'd go there today if I ever found myself in that part of town and in the mood for a burrito or taco salad. They're pretty inexpensive and the food is great. Very recommended.
Osha Thai Noodle House - I used to eat here with my friends. They really seemed to like it; I don't remember it being amazing or exceptional (I've long found infinitely better Thai restaurants, but they're much further away), but you might enjoy eating here. It's good for groups; it's more of a social kind of place with pretty decent Thai food.
Golden Era Vegetarian - One more for the vegetarians! This place is really amazing. Their fake meats will rock your socks off. If you go here, be sure to check out their crispy Lemongrass Chicken; it's insanely good and almost indistinguishable from the real thing. Served with broccoli and brown rice; probably one of the healthiest options mentioned so far. On the downside, this place tends to be a little expensive.
Community
