I'm using an EM 406A GPS module I bought from Sparkfun. It has 20 channels and locks on to satellite signals while it's in my apartment. My cheap TomTom can't. The Seeedstudio one seems to claim 32 (or 50) channels and such. Maybe I shouldn't be comparing channels but I don't know better.
Here is what I bought:http://www.sparkfun.com/products/465
They also sell a GPS shield for you to mount the module on. But I've got my own shield for that.
Here is a recent post I wrote:http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1292878749
The module is fairly small and nicely fits under a 16X2 character LCD.