In Cholla Bay, JJ's, the Old Boy social club just south of Play ground in Cholla. Xochillis cafe in Cholla? It is supposed to offer free wi-fi, last 2 times there nada.
Couple of places at the fish market on the Malecon.
A couple of the bars/restaurants on the Malecon have it (incl. Boo Bar)...it may be locked down but if you're there, they'll give you the passcode. Max's Restaurant off Calle 13 across from Penasco del Sol has had it for years. I think Capones has it. The coffee shop on Benito Juarez (main drag) in the area of the baseball stadium had it a while back.
Search your wi fi settings when you are at a place. If its available, they will ALWAYS give you the password. They want you to stick around and drink/eat.