Disclaimer: I have not received any compensation for the following; the opinions expressed are entirely my own (although I would not be averse to receiving comps should any restaurant owner feel so compelled... There are two criteria for inclusion: one, the place has to be good; two, the place has to be fairly inexpensive; three, the place has to be a "find": I don't include chains or well known restaurants. If you know a good place, suggest it to me; if I try it and like it, I'll add it and give you credit.
In no particular order:
V. Majestic (164 Brighton Ave, Allston; 57 Bus from Kenmore Square). Excellent Vietnamese food at good prices. Try their glowing beef or, for seafood eaters, their sea of Vietnam is an excellent mixture of oceanic edibles.
Chinatown Eatery (Chinatown, but I couldn't tell you how to get there: go to Chinatown and ask someone). Don't bother going to the upscale Chinese restaurants; this place has a dozen different establishments that will bring the food to a table you select. And if you want atmosphere, this place has it.
Beansprout (270 Medford Ave., Malden; a few blocks from the Malden Center T stop on the Orange Line). The only place in Boston where you can get real sweet and sour anything. One complaint: their white rice is not very good.
Korea House (117 Chiswick Road, Brighton; Chestnut Hill T stop on the B branch of the Green Line). The place to go for Korean food (although Korea Garden, below, ranks a close second). The difference between the two is the "other": the accoutrements of Korean food, like kim chee, and unidentifiable vegetable things.
Korea Garden (20 Pearl Street, Cambridge; Central Square T on the red line). If you're in town, a lot easier to get to than the Korea House, and just as good.
Porter Exchange (Cambridge, Porter Square T stop). Don't bother with the trendy, overpriced Japanese restaurants (including the one in the Exchange): go here, pick one of the "bars" (the noodle bar, the tempura bar, the sushi bar, etc.) and order what you want.
Sunny's Indian Restaurant (308 Main St., Malden; Malden Center T). Good Indian food, good prices, what more could you want.
The Skewers (92 Mt. Auburn St., Cambridge; Harvard T). Probably the best place to eat if you're in Harvard Square.
Cafe Jaffa (48 Gloucester Rd., Boston; Hynes Convention Center T). Close to Newbury Street; ideal if you're spending the day browsing the Newbury Street bookstores.