I'll be in Buenos Aires for about 10 days, Mendoza for 4 and Santiago, Chile for 4. Looking for some good restaurant recommendations. Doesn't need to be fancy! Just some great local places to eat. Any other recs for these cities would be great too...first time in all three.

In BA, Mercado De San Telmo (San Telmo Market).

In BA go to Tancot on Paraguay st. You get more for your money on Quality and quantity.

Advice to do a wine tour in Mendoza and ask to go to Azul and Carmelo Patti. He is the old rock star on Mendoza wine. We always do a wine tour, pick their minds then go back, if possible. Most of the time lunch is included.

Santiago has gone downhill due to the riots the last time we went. The central market is great with fabulous seafood. It does have great food but barriers were put in front to prevent vandalism. That's socialism for you.
Do your homework and pick a valley, Casablanca for Chardonnay, Maipu for Carmener(sp) and others.