And truthfully, there's some very impressive work being done in the indie demake quadrant - again, much of it stemming from The Independent Gaming Source's Bootleg Demake Compo in the summer of 2008.
So without further ado, I give you a small sampling of games dragged kicking and screaming into a generation of hardware limitations they were never meant for.
Megaman 4kb (C64 Demake of Megaman)
Hold Me Closer, Giant Dancer (Shadow of the Colossus Demake for the TRS-80 III)
Final Fantasy 7 (Demake for the NES)
Codename: Gordon (Half-Life\Half-Life 2 Sidescroller Demake, available on Steam)
Soundless Mountain II (Demake of Silent Hill II for the NES)
Portal: Still Alive (Flash-based Demake of Portal)
ASCIIpOrtal (ASCII Demake of Portal)
Super 3D Portals 6 (Atari 2600 Demake of Portal)
A list of the games being demade by the guys over at TIGSource can be found here, as well as the official catalogue over here.
And I would be remiss if I didn't mention the fantastic Gameboy demake mockups, in glorious grey\green\beige, by the folks over at wayofthepixel:
(Bioshock, by CroM)
(Psychonauts, by HMC)
(American McGee's Alice, by Arachne)
(Okami, by Doppleganger)
(Sam and Max Hit The Road, by KhrisMUC)
(World of Warcraft, by Arachne)
(Resident Evil 4, by Bouzolf)
And then, of course, you have the other side of the coin: remakes of retro games, a designation which apparently only requires that the game in question be updating to a platform released subsequently to the one the original came out on. Retro Remakes has a great list of remakes both current and in development. This deserves a post in itself, but in the meantime I'll leave you with this, from the as-yet-unreleased Maniac Mansion remake by German-based indie developers Vampyre Games (and which looks downright brilliant):