Don't get a postal vote: they don't send them out in time for them to be returned from overseas. Get a proxy vote, if you can, and appoint someone at your favoured party's office.
Labour: NHS, implementation of Beveridge report, Human Rights Act, Scottish and Welsh devolution, minimum wage, Racial Discrimination Act, legalisation of abortion, Open University, Health & Safety at Work Act, Civil Partnership Act, Kosovo intervention, reform of House of Lords, London Mayor.
Tories: Cones Hotline.
(Of course, OP only asked what great things have been done, not what crap ones have been done – there would be a lot longer list in that case).