I would highly recommend APRMedia (http://www.aprmedia.com), this has to me my prefered media supplier. They generally only stock the premium bands.
Digitalpromo (www.digitalpromo.co.uk) is also a reputable company I have used a few times before, as are Disk Depot (www.diskdepot.co.uk)
UKDVDR/Bigpockets/SVP/Big Maggot are all one company, trading as separate ones. While I have used these in the past, without problems, they can be known for poor customer service, and usually hold cheaper lower brand media.