Those MadAss bikes look really fun.
I still lust after a Confederate P120.
Also, a Hayes Diversified Technologies - modified diesel KLR650 is supposed to get amazing gas mileage, if you can find one in military surplus.
Ducati Monster Diesel is also a great-looking bike
And finally, a Rokon Trailbreaker would be fun. 2WD, wheels store gas, water, or act as floats for the bike while crossing rivers.