In recent days, two Flash-programmed replicas of old Macintosh computers have appeared on the radar. For your enjoyment:
Web SE
The better of the two, in English or German. A remarkably faithful rendition of System 7 with equally accurate software, right down to the After Dark control panel, and the MyEyes eyeballs that used to sit in the menubar and follow your cursor around. (Yes, this is the same one that Wired did a story about.)
http://myoldmac.net/webse-e.htm
P.dro Classic
Warning: IN FRENCH. Looks like it’s running System 6 on a Mac Plus or so. Not quite as polished as the Web SE, but the startup beep and drive clacking really adds to the experience.
http://www.erreur-404.com/classic-pedro.html
Update
There is also someone who has transformed a Mac SE into an ElectriClerk, just like from the Terry Gilliam movie Brazil:
http://www.ahleman.com/Props/ElectriClerk.html