All the standard ones are just fine in brackish water, and arguably better in brackish water than in fresh. They are certainly easier to keep in brackish water. Sailfin mollies and black mollies (at the very least) can be acclimated to fully marine conditions without any problems. Not sure about balloon mollies, since they're quite inbred and feeble.
The only molly you are at all likely to encounter as an aquarium fish that isn't a brackish water species in the wild is Poecilia salvatoris ("liberty molly") but I dare say it will do well in low-end brackish just like any other poecilid.