I have a linksys WUSB54G that really works well for me. It's powered by the USB bus, can be relocated very easily throughout the car, has great range and does all that other stuff you mentioned. I love when I pull up to a stop light and suddently I'm signed onto instant messanger. One time I was just going slowly through an intersection and I got logged on!
I think I got the WUSB54G for a bout $60 at CompUSA