I also have 2 DS 10, almost 15- in 2 days (and 1 DD)
The 14 y/o love the guys "perfume" like axe or old spice, plus batteries, batteries, batteries.
The 10 y/o like any small toys that I find in the bins at the Discovery Store, normally the squishy animal shaped things. He also still likes silly putty and magnetix.
For DD16

she gets girly stuff- hair do dads, makeup, individual packets of face masks, cute socks, cds, dvds. She's always been the easiest!!
For all 3 i try and find 2-3 different types of candy; 1 being "old fashioned" like pop rocks or Dip it, and the others are xmas kind you find in grocery store.
I do believe if I'm visiting WDW any time the year before I might pick up some tid bits from the candy store for the stockings (on the sly of course)
I'm glad I'm not the only one planning/shopping early. My DH thinks I'm crazy to try and plan so early.