Another old favorite, done in the wee morning hours in college when I should have been getting sleep before class, but inspiration struck.
I forget the details now, but some guy was trying to get together a freeware/mod remake of Joust and was soliciting concepts. Most of which--if I recall correctly, even an Andrew Jones concept in the mix--went back to the well of giant armor dudes, giant dragon-like birds. All pretty boring stuff. I wanted something lighter looking, more whimsical--and when I thought about it, I couldn't invent a bird as insane and wonderful as an ostrich, so I just went with that. Still holds up pretty well.