Do any of the rental cars have wifi?

Rental cars will only come equipped with whatever options the manufacturer includes for the model. These can vary quite a bit, and there are a few cars that are Bluetooth ready (such as the Prius) or have USB power jacks (most new Fords).

New cars with a satellite-ready radio often have 1 year of free service as part of the purchase, so these rental cars will have satellite radio in them (which is fun).

Some agencies also make GPS units available to rent for additional cost.

But I'm not aware of any vehicles on the market currently that have WiFi as an option.