In reply to Phizzers:
The Ireland select guide does a reasonable selection of the Mournes if you were going for one or two visits. Alternatively there is a comprehensive guide: http://www.bmcshop.co.uk/product_info.php?products_id=6037
I'm biased having grown up there, but the Mournes are great. Some really immaculate granite, huge number of climbs across the grades, beautiful surroundings, nearly always quiet. Much more impressive than Dartmoor, more variety and ease of access than Arran.