Someone or something having a disability.
In most cases, this is the term generally concidered acceptable among those with disabilities and is used in governmental and legal definitions. Naturally, politically correct zealots have taken offence at the overly literal (read: anal) definition and have coined empty phrases such as: Differently Able, dis-labled, handi-capable, mentally challenged, etc. If you are looking to be insulting, see: gimp.
See also: handicapped