I use an x-station. Love it, couldn't live without it. Can be battery operated for outdoor use. I use a G4 imac and didn't want the hassle + clutter of both an external card, midi out box and a controler keyboard. As a bonus it has a built in k-station synth engine. It is very reliable and novation customer support is exelent.
Mine you if I had the cash I would upgrade to a Virus TI polar which seems to be the same sort of thing but much better.