This page has a list of all individuals running for U.S. President in 2012 who have filed statements of candidacy with the Federal Election Commission, and who are Bylaws Sustaining Members of the national Libertarian Party.
It includes the following who have filed as Libertarians:
The following are Bylaws Sustaining Members of the national Libertarian Party and have announced their intention to run for U.S. President in 2012, but are not listed on the Federal Election Commission page referenced above.
*Information from LP.org*