I've written a program which simulates the motions of planets and other bodies. I'd like to run it on our own solar system, but to do so I need to know the current positions (preferably in heliocentric coordinates) of the planets as well as their current velocities. Is there a website where I can find this?
I've found all the positions of the planets here, and I can find their average orbital speed fairly easily, but for some planets (e.g. Mercury) the orbital speed varies a fair amount.