Arrived in Lisbon and sifting through the board for recs (thanks all for many great suggestions). I didn't see a post on this topic specifically so I'll start it here. The French have this term I love : bon rapport qualité prix--basically good quality / price ratio.
I'm wondering if we might compile a list of great budget restaurants in Lisbon and Porto. I'm thinking local, authentic and cheap places that offer great food at great prices. The kind of typical places with no english menus and speakers, where you just have to wing it in Portuguese and hope for the best. I'm sure some of the restaurants on vinhotinto's list or those mentioned in in other posts fit the bill, but I'm not precisely sure which ones. As I discover some, I'll post them too.