A lot of you people must be forgetting that this is for the "least favorite roster members"...not "how can you hate this character, they are awesome!". I kinda feel like if that were the inspiration for this thread, it oughtta be simple discussion threads for each character.
Meh...
Rachel Grey - Seriously, the reasons have all but been stated. Her arc, to me, ended when she disappeared in Excalibur 75 to save Captain Britain.
Storm - Just...I don't know. She's a strong black female character yet all she's doing now is serving as a foil to another strong black male character. While I enjoy the interaction, there's really not that many strong black characters in Marvel...I kinda would like to see them spread out more.
Nightcrawler - I love the character by design...but he's so boringly written anymore.
Iceman - Would somebody please just take this guy and give him something worthy of what his potential is? I've not been able to read him and his Polaris and Havok interaction. Gah.
Psylocke - It just seems like Claremont has been trying to shove her down our throats to me...it's really turned me off of her. The last time I really liked her was when she was coming on to Cyclops. Aaaaaages ago.
There may be more...but a great deal of them are in Uncanny and X-Men, and thank God I only read Astonishing anymore.