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

Concept art - 1
Character Viewer - 11
Ember Model - 21
Flame Model - 31
Sgt. Byrd Mini-games - 41
Spyro Turret Mini-games - 51
Sparx Shooter Mini-games - 61
Blink Mini-Games - 71