Up to date list as of Mar 08
Xbox 360 USB Compatible Devices:
Antec Notebook Cooler
Apple Keyboard (w/ Built in USB Hub)
Belkin 64mb USB Flash Drive
BUSlink USB 2.0 Disk On The Go/Lite (20GB and 40GB external)
Cannon Powershot A70
Creative Muvo 1GB MP3 player
Creative Zen MP3 Player (w/ firmware upgrade from creative.com)
Creative Zen Micro MP3 Player (w/ firmware upgrade from creative.com)
Data Traveler 1GB (thumb drive)
Dell 256mb Memory Key (thumb drive)
Fuji Digital Camera
Generic 256 MB USB Pen Drive
Hitachi Micro Drive 6GB (via CFII reader)
HP Photosmart 735 Digital Camera
Iomega 60 GB USB Hard Drive
iPaq rx3115
iPod (all) - AAC patch from the Marketplace is needed for iTunes.
iPod Nano - AAC patch from the Marketplace is needed for iTunes.
iPod Shuffle - AAC patch from the Marketplace is needed for iTunes.
iPod Video 5th Generation (Doesn't stream video, WILL work for audio and picture)
iRiver T-10
iRiver PMP-120
iRiver Clix
Pocketec (External USB) 40 GB Drive (Formatted in fat32 and 32gigs or smaller)
Keyboard - Basic USB
Kodak CX7430
Lexar Flash Jumpdrive (Should work for most sizes if not all)
Memorex 1GB Memory Stick
MS Natural Pro keyboard
Original Xbox Wireless adapter (MN-740)
PNY (1GB)
Rio Carbon 5GB
SanDisk Cruzer 256 mb Mini USB Drive
SanDisk ImageMate 12-in-1 Reader/Writer
Sony DSC-F707 Digital Camera
Sony
PSP (Playstation Portable)
USB Hub (4-way-connector has been tested)
Visual Land VL-340 1GB MP3 player / USB Thumb drive
VuPoint MSX400 Digital Camera
Zune