This bluetooth module seems to offer what you want.
It has USB but you can use RS232 instead (it has both) so you don't have to worry about host capabilities, you can actually connect this one straight to the MCU (since the RS232 voltage levels are already TTL).
The problem i can see is that this chip doesn't have much documentation. Here's what little information i found about the module - http://bdml0.stanford.edu/twiki/bin/view/Main/WirelessLinkOptions#UB1_1111_1112
At that price it seems there is no reason to try it out