This extension will automatically reset your invoice number when a new year starts. The invoicenumber is formatted like YOURINVOICEPREFIX-YEAR-number, so it will look somtehing like this "INV-2014-1". You need to have VQMod installed at your shop.
Tested with OC 1.5.5.1, but should also work with 1.5.1.3, 1.5.2.1 and 1.5.4.
Tested with OC 2.0.1.1 and 2.0.2.2, but should also work with 2.0.0.0 and 2.0.1.0.
Unfortunately I'm not able to give any support on this module. Feel free to modify the module to suit your own purpose.
NOTE: If you install this mod before the New Year's Day, insure your invoice prefix will be the same. Otherwise your invoicenumber will be reset because of the change of invoice prefix.