You can get good free WIFI at the McDonalds on the corner of Coba & La Costa. Also at Club Sandwich Cafe on Tulum but it only works well for some reason inside. And Starbuck of course at Hollywood Plaza, if you can get a seat. Have not tried to new Starbucks for WIFI at Paseo Cancun but assume it is available there too.
An update to this post: It looks like Starbucks is no longer offering free wireless. Was there yesterday and you have to do the Prodigy password thing. No matter. I prefer Buzz cafe and Fat Tuesday anyway!
Which Starbucks? Do they give you a code when you make a purchase or do you have to use your own Prodigy account?
The Starbucks...next to...Walmart! I am not sure - I think the street is Coba. They did not give me code but I did not ask. It looked like you could put your prodigy info in to gain access...