Amazon.com is offering the Linksys WPC54G for $66.49 with a $10 rebate direct from Linksys; Dell has a built-in rebate for about the same: I don't like to highlight deals, but this is quite a bargain. The Linksys WPC54G is one of the bestselling cards for 802.11g under Windows -- and Mac. (That's right: if you're a Mac user with Mac OS X 10.2.8 or later and AirPort 3.1 or later, you can insert this Linksys card to get 802.11g even if you can't handle AirPort Extreme.)
Follow the graphical link at right and add the card to your Amazon.com shopping basket to see the price. There's a link to a downloadable $10 rebate coupon. You can even use Amazon's super saver shipping and pay $0 for delivery in the U.S.
I checked out Dell's price on this, and they list the card at $63.95, but my account is a Home account, and they gave me 10 percent off for no good reason and free shipping because it was over $49. I'm not sure if everyone will see the same price, but the net is $57.56 without having to send in a rebate form.
You can compare prices for more stores for this item at Shopper.com.