Atomizer that's a great shot mate! Very dramatic lighting.
So, here's a recent one of mine:
http://www.users.on.net/~benhew/SG107642.jpg
I was experimenting with some gels on the flash. CTO (orange) gel on the flash, camera right. Sunlight camera left, crosslighting the subject. Camera white balance set to tungsten to render the orange light from the flash as a white colour, this gives the sky it's intense blue colour. Fun technique, I'd love to try it on a MTB shot but I'm not sure if my sync speed and flash power is up to it.
On another note, how good is off camera flash? I had a messy, messy night last night and just set up the camera and flash, left the flash on a bench bouncing it off the ceiling to capture all kinds of drunken shenanigans in a much more interesting way than the usual crap.