The program for Open House 2011 is online! It takes place from 7th - 9th October and looks very promising, though it looks to me like a smaller selection than previous years, and I'm disappointed not to see the awesome Iveagh House (aka The Dept. of Foreign Affairs) not on the list. I like the look of the walking & cycle tours, hopefully they'll get the weather.
Some highlights that I've seen before include:
The Casino in Marino
The Old Airport Terminal building
No10 Henrietta St
This year I would like to see:
The Iveagh Trust Museum flat
The French Ambassdor's House
The Military monuments of the Phoenix Park
The book was produced with the help of Fundit.ie this year and is available for free from all the usual places.