Personally, I love the program Alchemy, it's fun and a good pass time, but mostly used to sketching ideas out, or turning them into ideas.
(http://al.chemy.org/images/gallery/vorace/77vs4_thumb.jpg) --> in Photoshop (http://al.chemy.org/images/gallery/vorace/74lh7c_thumb.jpg)
features: http://al.chemy.org/features/ (http://al.chemy.org/features/)
download: http://al.chemy.org/download/ (http://al.chemy.org/download/)