GPS w/ Accurate Compass for Laptop

Hello all,

I'm looking for a GPS unit for my laptop. The main feature I need is
accurate compass readings, for which i can use to continually calibrate
my antenna. I know a number of systems provide a crude cardinal
direction compass system, but I was hoping for something a bit more
accurate. Some sort of elevation measurement would be nice too, but is
considered a bonus.

Price is more important than actual form. I imagine a dedicated GPS
unit /w computer interface would be mad expensive, and i have no
problems with a pcmcia or usb unit. I'd really prefer not having a
serial interface, I already have a HUGE number of serial devices.

Cost is kind of important...

Myren