I had an old Klein RASCAL that I stripped the paint off then turned into a single speed. Also had an Attitude. Both great bikes as they are stiff and basically a point and shoot bike that climbs and descends really well. Unfortunately it is too harsh for my weak lower back.
This SyCip singlespeed is a much forgiving bike and very comfortable on long rides:
But for more of a rockier terrain no holds bar ridin', I take this 29er BIG MAMA!
And if I want to go a 'lil lighter and climb all day, a ti 29er:
Even lighter for singlespeeding a ti Lynskey:
