I think the Gamecube should have sold much better than it did. At least N64 numbers. So many great games, a very affordable price and a beast of a console for 2001.
Also, another vote for the Turbografx-16 (PC Engine). If it had only launched everywhere (and a year earlier in NA) and if NEC had kept the design of the console like it was in Japan and just added a second controller port, its success might have carried over to the rest of the world. Great library of games and the best CD-ROM titles on the market until the Saturn/Playstation.