Many of you may jump on the Claremont bandwagon, but I have to admit, his most recent stuff has ruined his old stuff for me.  Theonly thing by him I seem to like by him now is The Hellfire Club/The Dark Phoenix Saga stuff. 
 
I kinda really like Mike Carey's run on Adjectiveless/Legacy.  Up until 200, it was amazing, and it slowed for a while but quickly picked up again and I'm really enjoying the title ATM.  Also really enjoyed some of the work by Craig Kyle and Chris Yost and Scott Lobdell.

I really enjoy Mike Carey currently, even with Greg Land drawing some of the stuff on Legacy but due to the fact I'm not as big of an X-fan on this website as some of the others are he's the best from what I've read.

Yeah, Greg Land....   *cough*

I always liked Scott Lobdell the best.
 
Phalanx Covenant. 
Legion Quest.
AoA.
Operation: Zero Tolerance.

Chris Claremont is still one of my faves.  
His recent faux paus' can't tarnish the great stories he wrote.
I love Morrison also.

Sorry, but this topic has already been raised:  Favorite Writer Run