A proper Star Control sequel would be awesome. SC3 was stinky. Seemed unfinished. And unbalanced - the Droog were too powerful.
Hired Guns was great, but probably superceded now to the point a remake wouldn't fetch you anything. Four player co-op shooting (and at each other too when the mood took!) like that would be fantastic of it's not out there already in some form.
A lot of Amiga classics would do well as remakes. Turrican springs to mind, as does Populous. God games have become too complicated. Nothings got the same appeal as Populous II IMO.
Going older, I don't think 8 bit titles have any gameplay that warrants a remake. eg. Atic Atac or Manic Miner/JSW, were great in their day, but how boring are they now?! All the fancy graphics in the world can't make a game more interesting than 10 minutes worth of fun. And if you change the formula to make it more fun, you no longer have a remake but a new game that just shares the name, like the latest Gauntlet versus the original.