You should be buying this: Superman?

What? Are you serious? Yes, amazingly enough. I've always thought that the Superman book was outdated, boring, unexciting, etc. The most interesting stuff I had read before these was 2 issues Joe Kelly wrote in the midst of Infinite Crisis (positing things that might have happened to the Earth-1 and Earth-2 Superman if Crisis on Infinite Earths had never happened). What happened was my Grant Morrison obsession lead me to All-Star Superman. Morrison's intention seems to have been to write fun, wacky, Silver Age style Superman stories without seeming stupid. I would definitely say that Morrison succeeded. Arm wrestling with Greek gods, crazy SCIENCE, Bizarro world (including a bizarro Bizarro who calls himself "Zibarro"), among many other things, Morrison has done amazing things with the character, as he is not restrained by pesky continuity.
Geoff Johns run on Action Comics has been a little different. I haven't read "Up, Up, and Away" yet, as I find the co-writer, Kurt Busiek, boring as hell. Most of Johns' run so far has been with Richard Donner (writer and director of Superman and Superman II), though his current storyline is solo. Of the two Donner stories, the first introduces the Superman II villains into regular continuity. Don't be fooled though, it's not just a comic adaptation of the second movie. The story involves a boy who falls to Earth in a spaceship and is surprisingly... Kryptonian. Superman immediately forms an attachment to the child, and tries to find some way to adopt him (while the Department of Superhuman Defense wants to study him). As it turns out, it is the child of General Zod. And he's found out a way to escape the Phantom Zone, as well as... all the other prisoners. Another story they did was too bring the Bizarro World back into normal DC continuity, which was taken out during the original Crisis as it was seen as being "too silly." The story was fantastic, containing the fantastic artwork of Eric Powell (the man from Goon). Johns' current storyline involves bringing the original Legion of Superheroes back into continuity (friends of Superboy back in the day), except, things are so fantastic in the future anymore... in fact, that's a Red Sun orbiting the Earth. That could cause some problems. Sadly, the collections for most of these stories won't be out til May in a collected form (though you could probably still find copies at your local shop) with the exception of the All-Star Superman hardcover, which is out now.