There's a little Mexican restaurant on Webster, just north of 14th street (next to the construction) that I'd like to recommend...
It's just recently reopened. I had walked by it for years, always disappointed that it was just a discarded shell of a restaurant... but two months ago they had an open sign in the window!
I've been there almost seven times now, and haven't been disappointed yet. It's quickly become my favorite Mexican restaurant in downtown Oakland. Standard fare of tacos, enchiladas, etc, but no tamales. Rice and beans are good, but the items are so amazing that I always order ala carte ($1.50-2 per item).
Meat options include chicken, ground beef, shredded beef, chile colorado, chile verde, and carne asada; I liked all but the carne asada (which oddly tasted boiled instead of grilled). The shredded beef is a bit barbecued, but makes for a mean tostada. Chile colorado enchiladas are great.
Atmosphere is almost nil. The restaurant is a night club on weekend nights, and it's up a creepy staircase (took a big effort to go in the first time!). And the service seems better on Fridays (early in the week, the cook is sometimes also the server; friendly, but obviously not used to waiting tables!).
Sadly enough, there are almost no patrons. Usually fewer than two other tables are occupied. But it was closed, and it's obfuscated by the construction. Still, they really need more patrons to stay afloat.