Recommended: Rosewill Wireless USB 2.0 Adapter 802.11b/g
I started looking for a relatively cheap USB wireless adapter that would work well with Linux.
After spending some time looking around and researching the matter, I finally bought a Rosewill RNX-G1 USB wireless adapter at newegg.com.
At $19.99, the Rosewill adapter, based on the Realtek RTL8187 chip, works perfectly under Linux on my wife's laptop. The increase in range, reliability, and speed over the built-in wireless was night and day.