To piggy back on Imperial Walker's nice siphoning thread, I thought I'd post a few pics and a description of how it is done.
The benefits are that the beer going from the primary (or secondary) carboy to either the secondary fermenter or keg, never touches air.
First, the parts, all available at a HBS for cheap:
Next, the transfer in action:
Essentially what is going on here is 2-3 psi from the CO2 tank is starting a siphon in the carboy. The beer is then pushed through the racking cane to the waiting keg. Simple.
I would have gone directly from my regulator but I didn't have the parts on hand, so I just used an empty keg (the small one) in between because those are the connections I did have.
I feel like Macgyver.