Specific guides
Multiple techniques
Articles by Phil Burgess on Adafruit
Animated Eyes
Electronic Animated Eyes by Phil Burgess, and another
Glowing Eyes
Lots of people have been making these for years, but here’s a video by Gryphern.
Animated Ears
Animated Tail
A really simple beginner’s tail by Phil Burgess
Non-electronic animated tail by Jinx_Tiger – I can’t find a reference to it online (Jinx’s technique goes back to 2004 or earlier), but it’s possible to make an animated tail that works purely mechanically. It’s the same general arrangement as what WolfTail does, with a string going up each side, but instead of servos doing the pulling, it’s attached to each shoulder instead. Move your shoulders and your tail moves.
More ideas
Haven’t looked for guides yet, but here’s some ideas:
Wings that open and close – I’ve seen pneumatic done, could be motorized or hydraulic as well, but it can be done purely mechanically as well. Not everything needs to be electronic.
EL Wire
LED claws
LED whiskers
LED’s under fur
Breathing smoke – e-cig parts