Keaton
I agree...bikes are tough to photograph since they are quite large but dont have that much visible surface area (esp. skinny steel bikes)...
like you said, you can shoot it with a portrait length lens wide open and use it to isolate the bike from the background....another technique is to combine that with a clean background...say set the bike up at the ocean, shoot from a low angle, so you have mostly the sky and clouds or the ocean in the back rather than some buildings.....
likewise you could bring the bike to the top of a big hill overlooking the city and getting an angle so that you can get a nice faded city background....
or, you can always shoot it macro or with a wide angle lens to really distort and emphasize elements of the bike (the wheel, the handlebar, etc.,)