For this thread, right now, with the folks that are here, and for the purpose of being educated in the discussion and posting that ensues, yes, Madoka is a must watch. But two years from now, we'll see. I'm also not 100% sure Champloo will stand the test of time, and I might've added NHK except I'm not sure everybody will see it and still be talking about it years from now. But yes, EVA, Bebop, maybe Clannads, some GitS, some Gundam, Haruhi if only to be able to appreciate Disappearance, definitely a few Miyazakis, either of Hasoda's features (Girl who Leapt and Summer Wars), one of Makoto Shinkai's (Place Promised, 5 cm/s, Voices of a Distant Star)... these are true anime must sees. Moe is a dime a dozen, though I love many of them, Lucky Star, Nichijou, but they're just for watching now, once, and then on to the next, not quite classics. Admittedly, I've yet much to see, K-ON, GC and other currents. Honestly, GL was great but... not forever great. CG was about the same, great but will be forgotten. Eden of the East at the same level. Then again, I said Beck and Smashing Pumpkins would be short-lived phenomenon... oh wait, I was wrong for about 4 years, and then I was right. Huh.
Edit: Holy ****, just starting Bokurano, and haven't even finished the OP and it looks epic!!! Report back after I've actually seen a few eps.
Edit 2: and the first guy I hear is Gintama's Shinpachi, boding even better (note my avy.) Reminding me a bit of Lord of the Flies. Also Ender's Game (seriously, if any of you who are at all into sci fi haven't yet read it, do so. A. Maze. Ing.)