I've got a Hawking PCI card from MicroCenter in Vienna, VA that set me back less than $30. Unlike most USB adapters in its price range it has a decent sized boom on it and a port to attach a bigger one if need be. If this is a desktop, just get one of these. It's cheap and Ubuntu supports it out of the box. The only card-specific drawback is that the Windows drivers are several years out of date, and, generally speaking, suck.
http://www.hawkingtech.com/products/productlist.php?CatID=19&FamID=33&am...
Here's the lspci output from the Hawking card, if you're still thinking about going down this road: 01:05.0 Network controller: RaLink RT2561/RT61 802.11g PCI
Uses the following modules, which ship with the stock Ubuntu kernels in Hardy: rt61pci 25472 0 rt2x00pci 11264 1 rt61pci rt2x00lib 22528 2 rt61pci,rt2x00pci
There is one major drawback that isn't specific to any one adapter, though. iwconfig et al are a huge PITA, complicated further by Debian/Ubuntu's underperforming networking initialization scripts. Though I finally do have /etc/network/interfaces defined well enough that it is finally reliably connecting to my WAP upon request, I find myself having to run ifdown/ifup on every boot - Might be able to fix this problem by moving the network initialization script further into the boot process, but I really haven't the slightest idea why.
Unlike competently designed systems such as Maemo (where seemless 802.11 functionality matters a wee bit more than Ubuntu powered laptops with wireless), Ubuntu causes far more problems running over a wireless connection (regardless of the card) than it does over a physical connection. The myriad poorly designed frontends to iwspy are similarly inadequate and, if you'll forgive the repetition, incredibly poorly designed. Don't even get me started on Xandros, and the Eee's half-assed attempt to find a better solution to the aforementioned problem.
In summary, you might end up with fewer headaches down the road if you just pull some CAT6, but the above card will work at least as well as, possibly substantially better than, any USB dongle.
Sean Crago Kathmandu