On January 8, Gallup Polls released its poll on how U.S. voters self-identify. For the fourth quarter of 2013, the two major parties together are only at 51%, a record low for them. See the details here, which show, for the fourth quarter, independents at 46%, Democrats at 29%, Republicans at 22%, no response 3%.
This poll does not give respondents an opportunity to choose “something else”, but past polls that have given that option find the “something else” above 10%.