Collect the indicated number of Dragon Eggs to unlock the corresponding option in the "Secrets" menu:

Concept Art: 1
Character Viewer: At least 11.
Ember Model: At least 21.
Flame Model: At least 31.
Sgt. Byrd Mini-Game: At least 41.
Spyro Turret Mini-Game: At least 51.
Sparx Shooter Mini-Game: At least 61.
Blink Mini-Game: At least 71.