Up for a real challenge? Fire up your http header sniffers, maybe even wireshark, and let's find out where the thumbnails are kept for video hosts.

YouTube is done, so let's find the rest.

(NOTE: if you are trying to paste code, replace "<" with "&lt;" and ">" with "&gt;"
Also, replace any ampersands with &amp; but don't do this if the code has already html friendly. -- KTHX)

(these are done)
YouTube
Google Video / MySpace video
LiveLeak.com / theOnion.com
MetaCafe / Break.com
iFilm video / DailyMotion
Revver / Vimeo
Yahoo! video / ComedyCentral
VideoJug / vSocial / ForaTV


[admin edit]
Crossed out video hosts that are now supported.