Payroll Software by Medlin Software - Version 4.2 - Revision 16 - includes all known state withholding calculation changes for 2010 as of 1/31/2010.
Oregon will have a withholding change March 1, 2010 (the specific changes have not yet been announced).
Arizona is changing to a withholding formula July 1, 2010 (the formula has not yet been released).