We recently stayed near Brecon and found the 3 Horseshoes Pub at Groesffordd which serves fantastic food and is very dog friendly. http://www.threehorseshoesgroesffordd.co.uk/
Another old favourite, the Bear at Crickhowell offered our dogs a bowl of cooked chicken on arrival which impressed them no end. http://www.bearhotel.co.uk/
I'm pleased to say that both appear in this on-line guide which seems to be a very valuable resource for dog owners. When on holiday I refuse to eat in pubs that don't allow dogs at least into the bar area.
http://www.doggiepubs.org.uk/index.php