Originally Posted by
Ascended
Hard to say, with only a limited idea of what you enjoy. But some of the classic I might recommend are:
Starman. By James Robinson, back in the mid 90's. It remains a cult favorite, had very, very, very few crossovers, and is collected in six Omnibuses which are pricey and worth every single penny. Starman remains a shining example of legacy characters done right, hits many of the themes that makes DC unique, and is considered by many to be Robinson's masterpiece (either this or Golden Age, which is also worth reading).
Manhunter. There have been several Manhunter series, but the one I speak of featured Kate Spencer, a lawyer in LA who got tired of super human criminals escaping justice on technicalities and takes vengeance into her own hands. It was published around 2006 by Marc Andrekyo (spelling is likely wrong), and shouldnt be too hard to track down in trade. Again, there are a handful of crossover issues but they're very few and very far between. This is a book that was cancelled two or three times due to weak sales but survived because of its loyal, diehard fanbase campaigning for it. If that isnt a solid recommendation I dont know what is. I actually discovered the book because of the first campaign, and became an avid fan until the end.
Green Arrow: Year One and Green Arrow: Longbow Hunters are both worth reading. Longbow Hunters was published in the late 80's by Grell, and while that story stands on its own, it started Grell's run on the character and that defined Ollie for a generation. And Year One, by Andy Diggle and Jock, was a stand alone origin story which, years later, would influence the development of the CW series (it is however, far better than the show).
If you want a walk on the whimsical, All-Star Superman, by Grant Morrison, is considered by many the greatest modern day Superman story and makes most lists for "greatest Superman stories ever". If you never understood the appeal of the character, give this a try. It's silly and over the top and full of emotion and intelligent writing; its bittersweet, funny, and provides a fascinating world that is bigger than life while also being incredibly small and vulnerable and undeniably human.
If you want something that no one has ever heard of, Breach. Came out in 06, lasted for a year, and was cancelled. It was meant to be a Captain Atom relaunch but became its own thing. I havent re-read those issues in almost a decade, but I recall it being lots of fun, with an interesting main character and a threat that was actually scary. But good luck finding it. Maybe if your LCS has a big back-issue supply or you use Comixology?
Going back even further, Hawkworld from the early 90's was damned good. Started off as a three issue prestige mini, ended up being continued as a monthly that ran for thirty-ish issues. Only one short Event tie-in, and otherwise it stands on its own. Really well done and it holds up surprisingly well.