A list of external game development studios (DS, Wii, 3DS only). We may also take a look at some outsourcing partners which Nintendo often relies on.
Asian studios they've worked with this generation:
Agenda
Alphadream Corporation
ARIKA CO.,LTD.
BandaiNamco
Camelot Software Planning
CING*
Denyu-sha
Eighting Co., Ltd.
fyto
Ganbarion
Good-Feel, Inc.
GREZZO Co.,Ltd.
G-Gadget Pte. Ltd.
Grounding Inc.
HudsonSoft*
Indieszero
iNiS
KeysFactory
MediaKite
Mitchell Corporation
Mistwalker
muu muu
Noise Inc.
Otodesigners co.,ltd
PAON Corporation
Q-Games Ltd.
RED
Sandlot
SEGA
Skip Ltd.
SquareEnix
SUZAK Inc.
syn Sophia, Inc.
Tecmo Koei
Treasure Co., Ltd.
Vanpool, Inc.
Vitei
Western studios Nintendo has worked with this generation:
Curve Studios
Factor 5*
Fuse Games* (Silverball Studios)
Headstrong Games/ Kuju London
Monster Games
Next Level Games
n-Space
Rare Ltd. (Microsoft Game Studios)
Zoonami*
*Defunct
This is odd: NoE says h.a.n.d. Inc. worked on PictureBook Games for WiiWare. Do you know whether they were involved?
Please add more as I certainly missed some.