Hi,
Depending on what you want to do, you have a few options as mentioned here.
First of all, you need to say, what is the maximum speed of communication you want to achieve? Is 115kbaud enough for you? Then you can go ahead and use the FTDI 232->USB conveter. If you are looking for a slower speed, then you can have the SiLab IC (I think their max speed is 19200, but may be wrong).
If you are looking for faster communication than that, you have a choice of using a parallell IC line FTDIs 245 chip or a other devices such as thosefrom TI or Philips.
The easiest way to connect USB to a u-controller is a RS232 to USB, you handle USB as UART on both sides and your life is much easier. The other solutions are slightly more difficult and need special programs/protocoles.
BR,
/Farhad