One thing I've noticed is that most all those "sexy" women's costumes in the stores are the perfect short-skirt length to wear bike shorts underneath.



But for inspiration, do a search for halloween-era cyclocross races or the singlespeed MTB championships:
http://3.bp.blogspot.com/_cYuQDS6aN0...00/Marvin2.jpg
http://blog.erdener.org/archives/ima...05-chicken.jpg
http://www.racingacrosstexas.com/halloween%20pic.jpg
http://www.flickr.com/photos/wanderi...7603361562649/
http://bp3.blogger.com/_pnf2noX8Zmo/...b1f2451b7a.jpg

-- gnat! (I'm gunna rig the 6-foot salmon outfit to work on the bike this year)