AVR-Chat

Try the MAX3110E spi uart.  Makes it simple to add as many real hardware
uarts as you need to any project.

Or, check out http://www.atmel.com/dyn/resources/prod_documents/doc2557.pdf
and just add as many mega8's as you need serial ports to your project.  It
is probably cheaper than the MAX part...

Having used the maxim chip, I'd go for option B.
There are some tricks to the max chip that are a bit non-obvious that you
don't have to put up with using AVRs, and you can also probably export some
of the application's "smarts" to them, and offload from the main processor.