After announcing recently that the individual return filing season would begin January 31, the IRS followed it up with a statement that business returns (non-Schedule C or E) will begin being accepted January 13.
(However, I usually recommend waiting a week after filing season opens to file returns, just to make sure any bugs have been worked out on the first line of fire.)
Corporate returns are generally due on March 15, but since that falls on a Saturday this year, the due date for forms 1120, 1120S and 1120-C will be March 17, 2014. Partnership returns are due April 15, as usual.