Maybe i'm wrong, but the default summons still reflect underdark stuff (rats...)
Maybe making default an animal theme (standard NWN, but weakened) would be better?
As for other themes:
Bird theme (regeants: feathers, bird beaks, harpie feathers, guano, etc.)
lvl1: chicken-turkey... low hp, low ac, low damage
lvl2: seagull-raven... low hp, higher ac, low damage
lvl3: hawk-albatros... medium hp, medium ac, medium damage
lvl4: eagle medium hp, medium ac, higher damage
lvl5: were-bird (harpie)
lvl6: were bird warrior (harpie upgraded)
lvl7: etc.
(Rats... Deep spiders, deep rothe)
Summon humanoid theme: (regeants: teeth, skin, hair, warts, etc.)
lvl1: skinny kobold
lvl2: cowardly goblin
lvl3: fragile elf
lvl4: sturdy dwarf
lvl5: raging orc
lvl6:drunk ogre
etc.
Tropical Island Theme
1) Gilligan
2) Parrot
3) Pirate
4) Sparrows Carrying Coconuts
5) Hula Girls
6) Drunk Surfers
7) Beach Bunny
8) Dire-Gilligan
9) Brazilian Girl's Volleyball Team