The I-95 Express Lanes in SE Florida don't charge tolls for certain vehicles, including registered EVs. Until recently, I thought that obtaining a FL HOV registration entitled you to the exemption, but it turns out you have to register for the Express Lane exemption here: http://www.1800234ride.com/commuter-options/registration-renewal-information/95express/95-express-hybrid-registration
. Note that there's no charge for this registration, but you need an HOV registration to register for the exemption.
Once you get the exemption (you'll be notified by mail), you're not supposed to mount your SunPass transponder when using the Express Lanes, otherwise you'll get charged. Unfortunately, that only helps people with windshield-mounted transponders (like me).