Currently Online 
Some of mine:
Solaris, Atari 2600
Pseudo-3D flight combat and a large explorable map would be ambitious by SNES standards; doing it on a freaking 2600 is madness, yet somehow, incredibly, it works.
Doom, SNES
Playing a PC showpiece on an ageing 16-bit console was downright surreal.
Resident Evil 2, N64
The original game took up two CDs; that they got it to fit on a 64MB cart while retaining the pre-rendered cutscenes, something hardly ever seen on the system due to storage limits, feels like a miracle.
Doom 3, Xbox
Like it's predecessor, another case of a game that pushed PCs hard somehow making the transition to much weaker console hardware.
Call of Duty: Modern Warfare 3, Wii
The original game was a late gen AAA PS3/360 game, something that had no business working at all on the overclocked Gamecube hardware of the Wii, but the devs made it happen.
