There are a number of datasets that you can purchase in addition to the Royal Mail PAF such as Multiple Residence, Not Yet Built, Companies House. Address Lookup prices start from £32.50. For a full list Register for a Free Trial Account.
You can also cleanse your data online to identify duplicates, gone-aways, deceased records and check against mailing and telephone preference services. Prices start from £30. For a free Data Cleanse Audit Register for a Free Trial Account.