The ralink chipset is the only wireless hardware to be truly FLOSS friendly, but alto the specs are available there are still issues with the drivers, and sometimes things aren't exactly straightforward.
This is the card I've got:

00:0b.0 Network controller: RaLink RT2500 802.11g Cardbus/mini-PCI (rev 01)

By default, with the old rt2500 driver I couldn't get it to work other than with wep or no encryption, altho WPA-PSK + TKIP seems to be supported. To get WPA2+AES you need the experimental rt2x00 driver and some handwork.
First of all the serialmonkey's forum is very active and helpful, please refer to it.
Second you need to roll your own kernel, because dscape/mac80211 patches in the ubuntu's stock kernel break the wifi stack and will prevent the driver from compiling. You can have a look at this link for guidelines on how to recompile a kernel the debian way. Once you're done, simply download the driver sources and follow the instructions in the README file. Just make sure you have the following in your rt2x00-sources/config:

CONFIG_RT2X00=y
CONFIG_RT2500PCI=y
CONFIG_D80211=y
CONFIG_EEPROM_93CX6=y

Everything else can, and should, be set to "n" (altho adding debugging support is up to you and stuff you enabled in your kernel).

The next step is to work out Master mode so I can use one of my boxes as an AP and bypass my crappy telco's one. If you are interested stay tuned!