Leaving out the dozen or so SF listens, my favourites of 2008 are:
Francis Durbridge - Paul Temple and the Madison MysteryPaul Temple and the Madison Mystery is a 'full cast' radio play, lasting four hours. The Bryant and May series by Christopher Fowler is narrated by Tim Goodman, Devil's Peak by Saul Reichlin and The Darkness and the Deep & Lying Dead by Cathleen McCarron.
Christopher Fowler - Ten-Second Staircase
Christopher Fowler - White Corridor
Christopher Fowler - The Victoria Vanishes
Deon Meyer - Devil's Peak (South African author in translation)
Aline Templeton - The Darkness and the Deep & Lying Dead