I had a post a while back about a skill simulator that a GW2Guru community member had whipped up. These are later revised versions in two flavors.
The Revgaming.net painterly themed version (giving tribute to the GW2 style).
The thing I like about this one is the inclusion of a trait simulator alongside the skill sim, so you can view everything in one window.
The French site Luna-atra took the updated version of the original skill sim.
This one is great because of it’s simplicity and quick to use layout. I usually head to this one when I want to just goof around with what is known about the profession skills. Also has the traits and downed/drowned state skills.