I haven't read any of the old issues of the series, I only got caught in from the movie, but discovered that the comic-verse was so much more better.
Naturally, the New X-Men storylines were good, I particularly enjoyed Cassandra Nova. But I can't pick up the New X-Men volumes at the bookstore, it hurts my head for some reason. I don't even bother with finishing PLANET X.
The Phoenix Saga should be mentioned, but lately I think Madelyne Pryor has a much more interesting and messed up life. Damn you, Scott Summers! Evil husband!
Astonishing X-Men's GIFTED storyline is great. Joss Whedon just knocked it out of the ballpark with his first X-Men gig. I think its his first.