Not sure of the working cards under expresscard but a quick search on google pointed me to this links. Search google for more.
For USB wireless I know certain Linksys WUSB54G "Wireless G" adapter with the Ralink chipset. Check this link for the ralink drivers plus many other choices. http://www.hpl.hp.com/personal/Jean_....802.11ag.html
Also D-Link DWL-122 rev.C1 uses the ralink chipset as well.
Find the ones you can get locally and search the HCL section here for them. Located at top or right. Lots of info on them there.
Also search here for them. There is lots of info here as well on google.
No idea on external antenna. Just have to search for them and see if they use something you are after.