The following list is by no means a comprehensive list. These are all devices that either we have tested ourselves, or that have been reported as compatible with ReadyBoost by others.
A-Data
A-Data SD, 150x 2GB
A-Data PD2 1GB
A-Data MyFlash 256MB
A-Data My Flash FP1 'Bio-Metric' 2GB
A-Data PD-7 1GB
A-Data PD-7 2GB
A-Data PD-7 8GB A-Data PD3 (Oriental Elite) 1GB
A-Data PD-7 4GB
A-Data pd5 512MB
A-Data PD-7 256MB
A-Data PD2 2.0 2GB
A-Data SD 1GB "150X" Turbo 1GB
A-Data PD-7 512MB
A-Data PD-7 16GB
A-Data PD2 2GB
A-Data PD9 2GB
Apacer
Apacer Handy Steno AH320 512MB
Apacer audio steno av220 mp3 player 512MB
Apacer Handy Steno HT203 200x 2GB
Apacer HT203 1GB
Apacer SD 150X 1GB
Apacer Handy Steno HT203 4GB
Apacer Handy Steno 2GB
Apacer 1GB Secure Digital Card 1GB
Apacer PD2 2.0 2GB
Apple
Apple Shuffle 1GB
ATP
ATP Petito 1GB
ATP ToughDrive 1GB
ATP 1GB SD 1GB
ATP Petito UFD (USB) 1GB
ATP ToughDrive 2.0 GB 2GB
AVB
AVB Rubber Drive 1GB
AVB UF2-4GA 4GB
Buffalo
Buffalo RUF2-E 2GB
Buffalo High Speed USB 2.0 Flash Drive (RUF-C2G/U2 ) 2GB
Buffalo RUF-C256ML-G/U2 256MB
Buffalo Clip Drive USB2.0 512MB
Buffalo RUF2-E2G-BK 2GB
Corsair
Corsair Flash Voyager 256MB
Corsair Flash Voyager (CMFUSB2.0-8GB) 8GB
Corsair CMFUSB2.0-4GB 4GB
Corsair 60x SD 512MB
Corsair CMFSD133-2GB 2GB
Corsair Flash Voyager 1GB
Corsair Secure Digital (SD) Superfast 133x 1GB
Creative
Creative MUVO TX FM MP3 Player 256MB
Crucial
Crucial Gizmo!Overdrive 512MB
Crucial Gizmo! Overdrive 2GB
Crucial CT512MBUFD 512MB
Crucial Crucial Gizmo Overdrive 2GB
Crucial Gizmo 256MB
Crucial Gizmo! overdrive 2GB
DSE
DSE Bullet Series 150x SD 2GB
DSE 512 512MB
Freecom
Freecom USBCard 256MB
Freecom DataCard 2GB
Freecom Freecom Databar 1GB USB2.0 1G
Imation
Imation Swivel Flash Drive 1GB
Imation i-Express (150x) 1GB
Imation i-Express 3 (60x) 1GB
Intuix
Intuix M300 U3 IXMMD2GM300U3 2GB
Intuix Smart Drive M300 U3 1GB 1GB
Intuix S300 U3 IXMMD4GS300U3 4GB
Kingston
Kingston SDM/2GBFE mini sd card and adapter 2GB
Kingston DataTraveler 1GB USB 2.0 (DTI/1GB) 1GB
Kingston Data Traveller Elite 1GB
Kingston Data Traveler U3 1GB
Kingston 50x elite pro SD card 2GB
Kingston Kingston Data Traveller II Migo 1GB
Kingston Kingston KUSBDTII+/1GB DATA TRAVELER II PLUS 1GB
Kingston DataTraveler ELITE 1GB
Kingston DataTraveler 256MB
Kingston Secure Digital ULTIMATE 2GB 2GB
Kingston SD/1GB (Standard SD) 1GB
Kingston Data Traveller DTI/4GB 4GB
Kingston U-3 Data Traveller 512MB
Kingston KUSBDTII+/1GB DATA TRAVELER II PLUS 1GB
Kingston DataTraveler 512MB
Kingston DataTraveler mini fun 1GB
Kingston DT Elite HS 2GB
Kingston Data Traveller DTI/2GB 2GB
Kingston DT1 - USB 2.0 2GB
Kingston Data Traveller II 1GB
Kingston Kingston Datatraveler U3 2GB Smart Drive 2GB
Kingston Data Traveller 2.0 / DTI/512 512MB
Kingston Data Traveler 1 1GB
Kingston Kingston Kingston Data Traveller II Migo 2GB
Kingston Data Traveller II (KUSBDTII/1GB) 1GB
Lexar
Lexar JumpDrive 2.0 Pro 256MB
Lexar JDSE512-00-500 B 512MB
Lexar Jumpdrive JDSP512-04-500C 512MB
Lexar JDFF512 Rev B 512MB
Lexar JumpDrive 2.0 Pro 256MB
Lexar JumpDrive® Lightning 2GB
Lexar Platinum II 80x Speed - Compact Flash 2GB
Lexar Secure 1GB
Lexar JumpDrive Secure 2000 256MB
Lexar JumpDrive 2.0 Pro 1GB
Lexar USB Jump Drive 512MB
Lexar JumpDrive® Lightning 1GB
LG
LG Silverline Edition 512MB Believed compatible (read on other forum)
LG XtickFlash 512MB
Memorex
Memorex Mini Travel Drive (U3) 2GB
Memorex M-Flyer TravelDrive 512MB
Memorex Unknown 512MB
Memorex Mini TravelDrive U3 2GB
Memorex mini travel drive 1GB
Memorex M-Flyer TravelDrive 1GB
Patriot
Patriot XPorter XT 2GB
Patriot Xporter XT 2GB Believed compatible (read on other forum)
Patriot 200X XT USB Drive 2GB
Patriot Xporter XT 4GB
Patriot EP+ SD Card 2GB
PNY Attache
PNY Attache Pro 2GB
PNY Attache 1GB
PNY Attache 2GB
PNY Attache 4GB 4GB
PNY Attache 512MB
PNY Attache 1GB
PNY Attache 512MB
PNY Attache 4GB
PNY Attache 4GB
PQI
PQI U339s 1GB
PQI USB DOM 2GB
PQI AE58-2030R 2GB
PQI U339 Pro 1GB
PQI PQI AE58-4030R 4GB
SanDisk
SanDisk SD Card 2GB
SanDisk Cruzer Micro 256MB
SanDisk Cruzer Mini 512MB Believed compatible (read on other forum)
SanDisk Cruzer Mini 4GB Believed compatible (read on other forum)
SanDisk Standard SD Memory Card 1GB
SanDisk Cruzer Micro U3 (SDCZ6-2048) 2GB
SanDisk SD Extreme III 1GB
SanDisk SanDisk UltraII 1GB
SanDisk Cruzer Micro USB Flash Drive 4GB
SanDisk Cruzer Titanium 1GB
SanDisk Ultra II CompactFlash 2GB
SanDisk SD Extreme III 2GB
SanDisk 512MB
SanDisk Cruzer Micro 1GB
SanDisk Cruiser Mini 1GB
SanDisk cruzer micro 1GB
SanDisk Cruzer Mini 1GB
SanDisk Cruzer mini 256MB
SanDisk Cruzer Micro U3 2GB SanDisk Cruzer Micro (U3) 2GB
SanDisk sdcz6-4096-e10 4GB
SanDisk Cruzer Mini 256MB
SanDisk U3 Cruzer Micro 2GB 2GB
SanDisk SD Card 256MB
SanDisk Cruzer Micro Black (SDCZ6-4096-A10) 4GB
SanDisk U3 Cruzer Micro 1GB
SanDisk Cruzer Titanium 2GB
SanDisk Extreme III 2GB
SanDisk cruzer mini 256MB
SanDisk Cruzer Micro 1GB
SanDisk Cruzer Micro 512MB
SanDisk Cruzer Mini 1GB
SanDisk Sandisk Cruzer Crossfire 1GB USB 2.0 Flash Drive 1GB
SanDisk Cruzer Micro SDCZ6-2048-A10 2GB
SanDisk Cruzer Micro 1GB
SanDisk SanDisk Cruzer Micro Black (SDCZ6-4096-A10) 4GB
SanDisk Cruzer Micro 1GB
SanDisk Extreme IV 2GB SanDisk cruzer 512MB
SanDisk Standard SD Card 2GB
SanDisk 1gb sd standard model (blue) 1GB
SanDisk U3 Cruzer Micro 4GB 4GB
SanDisk Ultra® II SD™ Plus USB 1GB 1GB
SanDisk cruzer mini 1GB
SanDisk Extreme III SD Card 2GB 2GB
SanDisk Cruiser Mini 256MB
SanDisk SanDisk Ultra II SD 2GB 2GB
SanDisk SD 1GB
Sony
Sony Microvault Plus (USM2GJ) 2GB
Sony MicroVault 512MB
Sony MicroVault 256MB
Sony Memory Stick Pro 512MB
Sony PSP-MP1G 1GB
Sony MicroVault Tiny 1GB
Sony Memory Stick Pro Duo(High Speed)MSX-M1GN 1GB
Sony 2GB
Sony MicroVault USM4GJ 4GB
Sony Memory Stick Pro Duo(High Speed) 1GB
Sony MicroVault Tiny 2GB
Sony MicroVault Tiny USM1GH 1GB
Super Talent
Super Talent 2GB
Super Talent Super Flash Drive 2.0 512MB
Transcend
Transcend TS2GSD150 2GB
Transcend Compact Flash 120x TS8GCF120 8GB
Transcend JetFlash™168 [Orchid] 1GB
Transcend JetFlash™168 2GB [Bamboo] 2GB
Transcend JetFlash™168 4GB [Blossom] 4GB
Transcend t sonic m3p player 1GB
Transcend 150X SD Card 2GB
TRANSCEND JET FLASH 110_2GB 2GB
Transcend SD 150x 4gb 4GB
Verbatim
Verbatim Store'N'Go 1GB
Verbatim Store 'n' Go™ USB Flash Drive - 2GB 2GB
Verbatim Store'n'go 1GB