In the past year I've been collecting some of the DC omnibuses.
So far I've got
Justice League Silver Age Omnibus v1-2
Justice League Bronze Age Omnibus
Adam Strange 1
Green Lantern 1
I also plan on getting the LoSH one and Green Lantern vol 2 when it comes out next year.
I'm not really into golden age stuff (it's the art mostly) but I'm really enjoying these silver age ones. I'd like Silver Age Batman, Superman, Aquaman, Green Arrow etc.
I love the story.
The evil Four are fantastic.
I also have Golden Age Wonder Woman v1.