Boy, I sure give the MAC MR4C some love. You would have to Ebay it or have a student discount to get it for less than $30, but even at $52 it is a steal if clearance is an issue for you.
It is the smallest current production ratchet that I have found, but it does have a really short handle if you are one who really torques on stuff (I'm looking at you, auto mechanics). For my purposes it is awesome. Our aviation maintenance shop (7 guys) have 6 of them between us.
I reviewed a bunch of 1/4" ratchets on my
blog
This is the only way that I have been able to make a thinner ratchet:
It is a Craftsman driver with a ground down adaptor.
Even this setup is barely skinnier than the MAC.