starkaat
Lift - Reach higher areas. Also could be used to go backwards over ledges, maybe.
Heat Shield - Walk through lava flows and stuff.
Lockpick, Invisibility, or similar - Dark type HM, used for sneaking around the evil team's bases.
(Mine are kind of silly, heh. I think the region features really affect what would be useful/interesting.)
All very helpfull though.
Do you mind if I use Lockpick and a modified Heat Shield? Maybe a lava surf type move? It's for a game I'm making and including all the regions will have me out of HMs fast.