I know it says 'best' but I can't choose between these four, two from a bent, two from the upright:
The finishing line of last summer's tour of Normandy (chasing a truck off the Newhaven ferry):
Chasing down a buddy on the Avenue Verte:
Resting up when the sunset got too beautiful to ride through.
End of a tour from Marble Arch to Arc de Triomphe:
Of the lot, the two from the upright are the risky shots. The first, because it entailed hanging way low on the bars and trying to steer through the viewfinder. The second because that day was the final 118 miles of the route, we'd been lost almost all of it, I'm on a sugar crash, exhausted, in at least 3 lanes of traffic, riding one handed, over cobbles, in fading light. I'm holding the camera with the wrong hand, and trying to avoid being killed by all manner of things.
The uprights were taken with a Minolta dSLR which has become entirely too precious to take on latter rides. The bents used a waterproof 10mpx point and shoot with a very handy interval shot mode.
I like the last image because it reminds me of a friendship, the experience, and how great it felt to cross that roundabout and get out of the saddle. If you've ever ridden a lightweight rigid framed bike with skinny 120psi tyres over cobbles at speed, you'll know this is exactly how it looks.
-Edited to use Flickr instead of awardspace as images weren't working.