Hey, Boulder. Few suggestions:
Right now, most mainstream comics are sub-par. Batman's weak, Spider-Man's mediocre, and Superman's just boring. If you really want some Superman, though, pick up All-Star Superman. There's only four issues out, but everything about it is classic Superman updated for a modern audience.
I also recommend the following in addition to All-Star Superman:
Astonishing X-Men. Best X-Men ever. It's written by Joss Whedon, the same guy who did Buffy and Angel. It's highly character driven, succint, and memorable. Very accessible as well.
Planetary. It's written by a guy named Warren Ellis, who uses this book to riff on pop-culture throughout the ages while still telling an incredible story about a team of "mystery archaeologists". It's set to end soon, but you can pick up the trades and any issues not already collected. Must be read to believed.
Ex Machina. It's about a guy who can talk to machines who's elected mayor of New York. Very relevant and intelligent, it juxtaposes his previous superhero exploits alongside his mayoral duties.
The Walking Dead. Like a long-term Romero flick in comic book form. Probably the best zombie story ever told.
The Eternals. Written by Neil Gaiman who is one of the two best writers in comics today, it deals with an elder race of superpowered beings adapting and living in the modern world. Only one issue out, so you can jump on.
Y - The Last Man. The best written comic book today, it deals with a man named Yorick, who, due to a virus which has killed all human males except for him, is literally the last man on Earth. Very feminist, but incredibly poignant.