See this site for a nice series of laptops and netbooks that come pre-loaded with any of several Linux distributions. All are guaranteed to work out-of-the-box. In fact, the company ONLY makes Linux systems.
the list at http://www.linux-laptop.net/ can be a little daunting, but it's a testamant to how well Linux had been adapted to running on laptops.
On a side note, I surrent run Linux on an Asus Aspire One, a Dell D830 (at work), and an HP TX1000, all without trouble.
Also, in case you were not aware, Dell does sell, on their website, some of their laptop models w/ Ubuntu pre-installed. If you want to avoid a big retail outfit like for what ever reason, another *great* company is system 75. They write custom drivers for the hardware in their laptops that is not well supported by the kernel, and provide commercial grade support for their laptops and drivers, and their prices are comparable to some of the bigger manufacturers.