Polyvore

Polyvore is a fashion, interior design and graphics creation website,
I use it make fashion sets based on a range of things.
so far my collection is pretty small as I'm new to it but some of the long time and well known users have hundreds of collections up and being viewed constantly.

It's not only good for the fun of creation but many of the more experienced users have launched their own groups that anyone can join.  These groups can be based on different ideas but you can join as many as you please and they hold regular competitions which the members can enter a 1 or more sets they have created - based on a stimulus e.g. the colour green, prom outfit or dream home.