Heads

• Foam
• Plastic Mesh
• Fiberglass
• Celastic
• Papier Mache
• Wireframe
• Vacuforming
• Thermoplastic Mesh
• Balaclavas
• Helmets

• Eyes
• Ears
• Teeth
• Tongue
• Lips
• Whiskers
• Nose
• Muzzles and Snouts
• Beaks
• Feathers
• Scales
• Horns

• Articulated Mouths
• Articulated Ears
• Articulated Eyes
• Voice
• Snarl Bars

• Taxidermy
• Electronics

Costume shop
Depending on how well-stocked your costume shop is, you may be able to get teeth, claws, and others of varying qualities.

• Nicodemus' page on body, paw and head construction - http://www.nicodemus.org/fursuit/des.php
• Measuring yourself for a hat, if your character has one(?) - http://www.villagehatshop.com/head_size.html
• Headmaking method using animatronics by Tioh - http://www.fursuit.de/cms/index.php/En:Fursuit_building (German version: http://www.fursuit.de/cms/index.php/Tioh%27s_Fursuit-Bauanleitung)