This is really great. (Here via umadoshi.)

I happily use my data plan at home, but when travelling on a pre-paid sim, I try to do everything I could to limit my data use. (Good tip for travellers: budget accommodation tends to have free password protected wifi, big fancy hotels do not as they expect guests to have expense accounts. this is something many people staying in hotels for a con have learned the hard way.)

One place I would definitely add to the list of reliable free wifi is Apple Stores, I have used their wifi on non-Apple devices with no problem.