We do run buses early enough to get you to an Early Entry for the parks. Also, a reminder, Taxi's are not allowed to drop off at the MK... they drop off at the TTC instead.
Checker Cab is the "official" cab of Disney... they are run by Mears, and are contracted through us, so you'll see them waiting at specially marked areas of the theme parks and the resorts. Mears also runs Yellow Cab (yet, strangely, they're orange...), Safety Cab, and City Cab.
By the way, watch out for immitations like Check-Her Cab, Check-It Cab, Check-Ah Cab, Check-In Cab, ... and yes... these are real cab companies. *sigh*