Greg A. Harris was a fairly well-known switch pitcher in the 80s, although he didn't do it in a game until the 90s, for the Expos IIRC. Bert Campaneris also did it for the A's, in a game where he played all nine positions including pitching left- and right-handed.
The Braves had one in their system about five years ago I think; he never made the majors.
I know there's another one that's slipping my mind. Most teams are reluctant to let a guy do it, even if he can. Most of Harris' teams wouldn't let him, mainly because the need never really came up ... it would have been more of a stunt than anything.

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