I was playing with one of my FTDI FT232R USB to serial converter chips last night. Really nice device. Not only does it have a serial port that will run at up to 3mbps, but it has a full set of handshaking lines; and any of the eight serial port lines can optionally be inverted.
If that was not enough, it has five additional I/O bits, four of them can be used as general purpose I/O, or be assigned one of many alternate functions – including outputting a 6/12/24/48 MHz clock! It also has a “bitbang” mode that I will explore later.
You can also use it to draw power from the USB cable, and power the electronics you attach to the FT232R – mind you, you really should not draw more than about 70mA from the USB cable to leave plenty of power for the chip.
You can read more about the FT232R HERE.