Having spent many an hour holed up in the fort at the end of my parents' back yard, I greatly appreciate the small get-away that a play house provides for a child. I could conquer zombies if they came, have a snack or even make signs to keep out boys (and their cooties). 20 of our recent play house favorites are after the jump!
Play Houses Listed Above are Bolded Below, Left to Right
• Andrew's Simply Awesome Playhouse
• Look! Ruby's Playhouse
• Look! Handmade Willow Playhouse
• 4-Sided Felt Play House Slipcover
• Modern Playhouse At Dwell On Design
• Sophie's Nova Scotian Playhouse
• Collapsible Indoor Playhouse
• Cardboard Playhouse from Anthropologie
• Color Me Cardboard House
• Built-in Indoor Playhouse
• Building Plans for StudioMama's Kids' House
• Little Crooked Houses
• Lilliput Play Homes
• Look: Turkey Feathers' Playhouse
• MetroPlay Playhouse
• Mobile Home by Kids on Roof
• How To: Make A Willow House
• Drool Worthy Tree House Play Room
• Extreme Home Makeover Little Tikes Edition
• Another Little Tikes Home Makeover
(Images: As Linked Above)
Small Cool Lessons: Discovering Small Space Design Ideas That Really Work
Beatriz's Fun & Functional Workspace
Good Food to Share 
The Big Book of Small, Cool Spaces 
Apartment Therapy Presents 
The Eight-Step Home Cure 
Sheex Bedding
How to Make Easy 3-Ingredient Energy Bars at Home
How to Make Fresh Pasta Dough in the Food Processor
Love the play houses! My daughter is very lucky, she's going to inherit her cousin's play house. It's very similar to but a bit bigger than Sophie's Nova Scotia playhouse, and has a drywalled interior, but it needs painting.