Here's a list of sites that offer many ideas for creative kid play.

infant/toddler play

Preschool outdoor play

Preschool party play for young children

Kids games

Kids running games

Kids exercise

Outdoor activities for toddlers

Preschool "Olympics"

Backyard games

Teacher-tested ideas for outdoor fun

Enhancing outdoor play areas

Planning for outdoor play (from HeadStart)

Quality in outdoor environments for child care

 

Articles/research about play

What young children learn as they race around the yard in fantasy games

Making the most of outdoor time with preschool children

The importance of outdoor play (great photos!)