Have in the past painted my carport cement floor with just simple grey latex paint.
Lasted for awhile. But the car tires peel some of the paint away.
It there was a clear protected coating you could roll after the paint dried
That would be great.

Latex is not a good paint for exterior concrete. Rust-oleum makes a good paint for a slab. Most of us will recommend an epoxy paint which is mixed with a catalyst. RustOleum.com (http://www.rustoleum.com/CBGProduct.asp?pid=16)