There was a mention in this week's MCN of Walt Siegl Motorcycles, who are doing interesting things with air-cooled, two-valve lumps. I had a look on their website
http://waltsiegl.com/motorcycles/ and their output is pretty impressive. I certainly wouldn't complain if I found any of these three under my tree next week!
Nice, clean simplicity. DS motor.
Shades of an old '75 900 SS here, I think.
Very reminiscent of the Cagiva Elefant, again with a DS motor. The website claims a 154kg kerb weight and with 21"/17" wheels, it should have some genuine off-road ability. It'd certainly be fun to try anyway.