I have an Excel file with formulas in this manner:
=IF(OR(ISERROR(G16),ISERROR(G17)),X16,IF(OR(G16=\"xxx\",G16=\"yyy\",G16=\"zzz\"),Y16,IF(G16=\"333\",\"N\\A\",IF(
You can use Alt+Enter in the formula bar to make your formula multiline. Sadly, no tabs only spaces so it becomes tedious to create and edit. See also
http://www.dailydoseofexcel.com/archives/2005/04/01/excel-formula-formatter/