Now Joshua has written up an extensive report, Cycling Ireland, 1994, which includes (off-line) pictures
As a general guide to Ireland, the guide from Lonely Planet is the best I found. I can't be sure since it's on loan, but if it's like most of their books the title is Ireland: a Travel Survival Kit. It's very detailed and practically-oriented, though not (IMHO) as good as LP's India: a Travel Survival Kit.
Being from the Seattle area, one of the most useful accessories I can think of is one of the little one-shot espresso makers available from REI and other sporting goods places. Good coffee is hard to find in Ireland, and I do like my morning cup or two. The cast aluminum espresso makers work perfectly on my MSR stove. They're smaller than a regular camping coffee pot, and have no moving parts -- well worth the extra space in my luggage.
Speaking of camping and cooking, if you are taking your own stove along, it's a good idea to take one that runs on auto gas, since kerosene and stove gas are hard to find in many areas.
My favorite area for riding was definitely the Pacific coast north of Sligo, up to Bloody Foreland. The old coastal road is very hilly, and the pavement could use some work in spots, but there was less than a tenth the traffic of the main road, and the views are incredible. There are quite a few good hostels along this stretch of coast, and countless B&Bs. If you're feeling more adventurous, there are plenty of places to camp, too. I weathered quite a storm on Bloody Foreland, getting my tent set up inside a fallen-in stone house just before the gale-force winds filled up with rain. As the gloom darkened I sat with a roll of digestive biscuits and a cup of port listening to the crashing waves, hoping for fair weather in the morning. The sun rose in a clear blue sky, which stayed with me all day on the road to Letterkenny.
Another beautiful area was the Wicklow Mountains and the lowlands to the south of them, though that was much more crowded, even in the early off-season.