I absolutley love Polyvore.com! It's an amazing artistic outlet for those of us who are not particularly skilled with paint and a brush.
Polyvore is a free web-based application for mixing and matching images from anywhere on the web. Its main claim to fame seems to be its collage functionality for creating fashion ensembles, but it can really be used for anything - interior design, advertising, holiday cards, and simply creative collaging.
You can also browse other people's sets and import your own pictures (either personal or from the web).
WARNING! This site is HIGHLY addictive! :)
Below are some of the collages I created.