This book gave a great overview and some routes through Ireland via bicycle. As I still have not totally planned my trip, I cannot tell how the recommendations are, but Lonely Planet guides are usually been excellent, in my experience. I wish it had more information on choosing between a guided and a DIY tour, as I am now trying to decide whether to do all the work in carrying luggage, making reservations and finding bikes B&Bs myself, or spending a little extra. It has good information about bicycles and the gear to bring along as well.