The best example of this would be the Video Toaster: http://en.wikipedia.org/wiki/Video_Toaster For much of the 1990s, it was the king of real-time broadcast video production, unsurpassed until the advent of hardware-accelerated PC graphics late in the decade.
They were good for high end graphics and video of that era but I think SGI quickly caught up and surpassed them there. The other bit about Amiga that seems to be forgotten, just how proprietary the hardware was. We had a floppy drive go out and, to this day it remains as one of the more difficult to get to parts of all the computers I have had to crack open to replace a part in.