For desktops, getting a wireless card that works "out-of-the-box" in Linux is very easy. See
this NewEgg search. I make all of my desktops from parts I get from NewEgg.
With just a little effort, I've put together some amazing machines with lots of power, and
five fans per machine to keep everything super cool and long-lived, at a remarkably small overall sticker price. And it's
really fun putting together a desktop. And--this is a secret the OEMs don't want you to know--the warranties on parts from the manufacturers typically greatly exceeds the standard warranties offered by the OEMs. I have four desktops in use in my home that I made from parts I bought new from NewEgg. My main personal machine (details in my signature) has run almost 24/7 for almost four years and still works like the day I put it together. Three of the four desktops have very inexpensive wireless cards (around U.S. $15) because it's MUCH cheaper than running cords throughout the house.
For laptops,
see this page.