doogal.co.uk has some exciting new postcode data (depending on your definition of exciting…). I’m in the process* of importing population data for each active postcode in England and Wales. This includes the estimated population and number of households and comes from the ONS website based on the Census of 2011, which I’ve just realised only covers England and Wales. Scottish data is a separate download and will be my next task. Northern Ireland doesn’t seem to provide population data per postcode.
The data appears on the information page for each postcode and will become part of the CSV downloads once the import is complete. I could aggregate this data up to postcode district and sector level, so let me know if that would be useful to you.
* A database of 2.5 million postcodes can take some time to update!