First of all if you're a Chicago resident and you haven't purchased a single speed yet, just Google the "Mongoose Sinsure".
Get several feet of duct tape. Paint the duct tape matte black or dark brown. Wrap the down, top, and seat tubes with the painted duct tape. Find an old, comfortable, and butt ugly saddle. Replace the original saddle with the butt ugly one. Purchase a thick U Lock. Preferably one that's at least as good as the OnGuard U Lock.
Best Wishes and Good Luck!
This post was originally intended for those Chicagoans who have to lock their single speed bikes up outside, overnight. However, it's really for any Chicagoan who has to keep his bike locked up outside for extended periods of time.