I wouldn't bother. With the exception of the odd issue here and there, Superman comics haven't really been worth reading for the last 10-15 years. DC have managed to completely wreck almost every aspect of the character, and it's no coincidence that Superman comics rarely crack the top 50 anymore.
There have been some pretty good out-of-continuety one-shots, though. I thought it was very overrated, but All Star Superman was extremely popular, and I'd certainly admit that it's a masterpiece compared to the regular comics.
Superman for all Seasons is a great 4 issue mini-series, dealing with the early days of Superman's career.
Secret Identity is a Superman story that... kind of isn't really about Superman, but still manages to be one of the best Superman stories ever.
Those are all available in trades.
I'd also recommend the Death and Return of Superman. There's an omnibus collecting the entire series of Death of Superman, Would Without Superman, and Return of Superman, which can also be found in individual trades. Not quintessential Superman, but quite a thrilling read in many ways.
If you insist on trying some of the newer stories, I guess the first few storylines of the Superman & Batman title weren't too bad. The first one, Public Enemies, was a bit hit and miss. Supergirl was quite good, if you ignore the idiotic ending, and it was a relatively worthwhile title up to and including The Search for Kryptonite. These are also available in trades.
I know it's not really what you asked, but I'm just trying to keep you from making the mistake of diving into the garbage that passes for Superman comics these days.