I can't remember what is was called, but it was this JRPG for the PS1 that completely reinvented the genre and made it commercially successful. People like it a little less these days, but for most people it still holds up. For the life of me, can't remember the name, but I think it would really do good with a graphics update, even by PS1 standards for graphics it hasn't aged well.
Seriously though.
Xenosaga needs it because, if nothing else, those games are not cheap, and they're not particularly easy to find either.
There are still a few fighting games that would do well with an upscale to HD graphics and online play: the Street Fighter Alpha series, particularly the second one, Capcom Vs. SNK 2, and Vampire Savior.
I would also pay $60 for a simple port of Terranigma with the graphics drawn over like for Super Street Fighter II Turbo HD Remix.
The Legacy of Kain series would also be great.