I'm predominantly a DC guy. Always have been. Likely always will be. Naturaly I've read some of the must read Marvel books, Miller's Wolverine, Daredevil Born Again, most of Civil War. I have Runaways, but haven't got around to it yet. What else is must read trade? Classics or new, I wish to expand my horizons a little.
If you liked Kingdom Come or the retro-iconic feel of such a title, you should read Marvels by Busiek and Ross. If you liked New Frontier you might like something like Thor The Mighty Avenger by Samnee. If you like Simone and Secret Six you might like Simone on Agent X (and if Udon strikes your fancy trying Taskmaster 2002 and Deadpool from that era) or something like the Thunderbolts. With the TV series coming you might want to try Alias, The Pulse, and other MAX titles like Punisher.
Nextwave is a must read comedy series and David's Defenders and Slott's She-Hulk are funny. Some find the "Punisher Kills" runs to be funny. The short New Warriors run by Wells was funny and referenced in Civil War.
New Avengers (Bendis 2004) was sort of Marvel's return and a core team of A-listers (comparable to Morrison's JLA). Speaking of which, Grant Morrison's New X-Men introduced a bunch of landmark X-Men stuff and is a bit off-beat... if you like the odd-ball additions and twists and turns Morrison's added to Batman in the last few years, he did much of the same for the X-Men. Whedon did a character driven Astonishing X-Men run that's well regarded... and much of X-Factor is pretty consistent.
The latest volume of Punisher by Rucka is similar to Gotham Central and the prior Ennis volumes feels like Ennis' Vertigo work somewhat. Loeb and Sale did Bat's Long Halloween and Superman's For All Seasons but also a series of Marvel books including Spider-Man Blue, Daredevil Yellow, etc. If you liked Great Ten you might like Iron Fist....
If you like the JLA or their deconstruction in things like Authority or Planetary, you should consider the Supreme line of books. If you like Suicide Squad or similar books consider Uncanny X-Force. Last, and certainly not least, if you've read and enjoyed Waid's distillation and crystallization of superheroics in the past, you will probably like Daredevil.
There are many many many more Marvel books (given they released nearly 72 titles a month in 2010, the sheer volume is staggering) but this should be enough to start... if you have any specific tastes, let me know.