Just things with Superman in them, I'd recommend JLA/Avengers.
Superman is especially prominant, along with Cap. In general it's a must see event for being a genunely epic feeling event, that managed to be fun. You can almost call it a cap on comics before the New 52 broke DC..
All-Star Superman [Morrison]
Superman Beyond [+Final Crisis] [Morrison]
Superman: Secret Identity [Kurt Busiek]
Superman: Red Son [Mark Millar]
Up, Up and Away [Kurt Busiek & Geoff Johns]
Superman: Last Son, Legion of Super-Heroes, Brainiac by Geoff Johns
Superman: Birthright [Mark Waid]
SUperman: For the Man who has Everything [Alan Moore]
Superman: Whatever Happened to the Man of Tomorrow? [Alan Moore]
Action Comics 1-16 [New 52] by Grant Morrison
Superman: For All Seasons [Jeph Loeb]
“Perhaps this is the ultimate freedom. The freedom to leave.”
I actually find Superman a little boring when he's just alone or paired with only his own supporting cast for too long. (There are some exceptional stories that are exceptions to this.)
So I'd primarily look at arcs where he has the company of other heroes.
Superman / Batman stories are among the best--they really play well off of one another. However, the good ones are the ones where Supes is shown as a capable and strong personality, able to match Batman as a MAN. There are some disappointing stories where Superman is basically treated like a child by Bats.