Some firms offer basically a 3/8 ratchet body with a 1/2 inch square drive (similar idea to the more common 1/4 ratchet with 3/8 drive). Think Hazet offer one. There are probably others!
Nepros have recently offered a version of their 90 tooth ratchet in 1/2 drive, which I havn't seen but has got to be pretty sleek!
Failing that, if you can wait a little, KoKen are introducing a 1/2 inch drive version of their Zeal / Z Series. I have the 3/8 ratchet, and if the 1/2 inch is as good this will be a serious contender. Matching low profile sockets will probably be helpful too!