I get more split ends during the summer, but I recommend anything that adds moisture to the hair: Humectress, Lacio-Lacio, Moisture Maniac and I recently added KeraKare Humecto to my list (CaramelHonee has been raving over this stuff for ions).
I find that if the hair has been left w/o a decent trim, then the splitting goes further up the shaft. As many know, I'm a huge advocate of dustings, but dustings are only preventative, where as trims are more of the cure. Maybe you could try getting a really good trim, have your styilst do small sections at a time, rather than trying to trim all of your hair at once. Then try maintaining that with dustings.