There's a lot of published material out there, good and bad, official and third party, for many different game systems.
I'm the proud owner of many adventures, accumulated since I got into tabletop 15 years ago. However, I am but one mortal with so much time left on this earth. I may run them all at some point in time, but even then I have priorities. I'd much rather plumb the depths of an iconic dungeon than some bland low-level "kill the goblins in the cave" scenario we all done a million times before.
I played the Red Hand of Doom, am participating in the (highly modified) Dragonlance Chronicles, and DMed Shackled City and Age of Worms.
What is your adventure wish list? What modules have you not played in or run, but would like to do at some point in your life?
It doesn't necessarily have to be Dungeons & Dragons. Other systems are fine, but then again, most in my list are D&D, Pathfinder, or some variation. Other adventures in tabletop just aren't as well-known and iconic.
Rappan Athuk: Cuz this is the megadungeon that appeals to me the most at the moment.
Snow White: A fairy-tale-themed adventure path/series made by folks who specialize in making adventures. Might be fun to GM such a world.
Sword of Air: A mega-adventure sandbox by the Rappan Athuk guys. Is very non-linear and location/hex-focused, but has a main overarching plot which the DM can reintroduce and fade away depending on player interest. Unlike many other "old school" style adventures, it has high stakes centered around an eponymous artifact with two feuding archmages involved. Has chances for heroism on the PC's part.
Way of the Wicked: I hear a lot of good things about this one. Combined with several actual play reports and advice, the idea is novel enough (evil campaign) to at least try.
Zeitgeist: Fantasy not-Victorian England with PCs as royal agents for queen and country? Sign me up!