The guy who wrote Civil War has done several other great series. Firstly The Ultimates 1+2 (there was an ultimates 3 but it's by different people and it's awful) which was taking the Avengers and then updating them both to avoid the mountains of old continuity and to modernise in.
He also did a superhero series called The Authority which was great in either Mark Millar's or Warren Ellis' runs, they can be hard to track down but they're worth it.
He's also done a ton of his own series including Wanted, Kick-Ass and Nemesis which I personally like but alot of people hate.
Also read Watchmen, it's by two of the best people to ever work for 2000 AD and it's widely considered the best superhero comic ever.
Beyond those there's alot more but you haven't given much indication of what you like so I'll start with great stuff by 2000AD writters
Nemesis the Warlock, The Ballad of Halos Jones and Future Shocks. These three all ran in 2000 AD and are the best of it's early stuff, they've all been collected (look out especially for Alan Moore's Future Shocks) Nemesis kinda goes downhill in the second volume but the first is great.
Now the best 2000AD writer is Alan Moore, aside from Watchmen he's done V for Vendetta which is great as well as Miracleman which is even better. V is easy to get and has some of the best art of any comic ever. Miracleman's art conversely hasn't aged well and due to copyright issues it's almost impossible to get without spending silly money, you have to torrent it which obviously I can't condone due to forum rules. He's also done The League of Extraordinary Gentlemen (with an artist from 2000AD)now the first two volumes are must reads but the later stuff (Black Dossier and Century) move away from te Victorian stuff and contain much more sex and weirdness some like them some don't. He also did From Hell which is a weird and brilliant tale of Jack The Ripper, the art isn't great but it might be worth checking out. He's also done Supreme and Top Ten which are both good but not must-reads, if you like his other stuff check them out. Oh and he did Neonomicon, you can ignore that.
Neil Gaiman who wrote for 2000AD has to my knowledge only done one major comic series which is Sandman. Now Sandman is possibly the best comic series ever. There are 10 volumes plus a couple of extras all of the are worth checking out, the art is less than great for some of them but the writing is always superb.
Grant Morrison did Zenith for 2000AD but I've never read it so I can't say if it's any good. What I can say is good are Animal Man, Doom Patrol, The Invisibles and The Filth. Now these are all very weird and sometimes very disturbing, he heavily uses crugs, postmodernism, dadaism, litterary refrences and just general weirdness. Some people find his work pretentious and incomprehensible but I think they're great. Invisibles is probably the best but the others are also good. He's also done Flex Mentallo which is just a giant pile of WTF (but with good art) and Arkham Asylum which is him applying oldshcool psychoanalysis to Batman, this has brilliant art but is really hard to understand, worth reading if you find the idea of scenes symbolizing Batman's repressed homosexuality entertaining.
And last but by no means least Garth Ennis, he's written some of the best runs on Judge Dredd and The Punisher, both of which are easy to find. He's also done a ton of smaller series including Hitman, Crossed, various World War 2 conmics and a ton of other stuff. His best series however are Preacher, which is about a Texas preist going out to find God, it's very good but to just give you an idea of the tone of the series there's a major character in it called Arseface. His other best series is The Boys which is superheros series done by someone who hates superheros, it's very good with great art (mostly) but it does have alot of moments where when reading I just stopped and thought "Why would anybody ever write that?". So it's good but just make sure you can handle some really messed up stuff.
