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
AML MT7550 (review on linuxdevices.com): computer in a robust case, with a touchscreen. Intended for vehicle mounting (forklifts etc.). Default install Debian etch.
Nokia 770: The Internet Tablet uses a Nokia-specific, Debian based Linux distribution. Not pure Debian, but close enough.
Groovix: Debian-based PCs, configured for up to 10 simultaneous consoles (yes, physical ones!)