Various vendors will pre-install Debian on hardware that you can buy from them.
A short list of products that ship with Debian pre-installed:
Lemote Fuloong 2F Mini-PC uses “红旗 Linux/Debian”
NETGEAR ReadyNAS shipped with sarge and a modified kernel
Aleutia E2 low power desktop PC shipped with Debian etch on one flash card
http://www.embeddedarm.com/products/board-detail.php?product=TS-7800 TS-7800 ARM9/FPGA developer board
Moxa Communication-centric RISC computing platform UC-8100-ME-T
A list of pages where Debian derivatives list products shipped with the derivative preinstalled: