Depends what your other needs are. If you want to record multiple inputs you'll need either an Mbox2 or Mbox2mini and an outboard mixer, or if you dont and dont need mdi ports for a synth then you can use the mbox2mini.
its cheap, comes with PT and a decent ignition pack full of free stuff.
the convertors on the mbox series are pretty good as well and they're a whole lot cheaper than the maudio ones.
Pro-tools cards are just soundcards and work with any program under osx, i run logic 8 and Ableton and system sounds etc with my mboxes without any problems whatsoever.