There are a number of Hundertwasser books out published by Taschen, but the bargain of the century is the 400-page edition "Hundertwasser (Hundertwasser - 1928-2000)" by Wieland Schmied. One of Taschen's 25th anniversary printings, this is a poor-man's copy of Volume I of Taschen's two-volume limited edition (of which only 10,000 copies were produced). Hundertwasser worked closely with Taschen on this (designing the layout himself), and the text for Volume I is by Schmied, an art historian and longtime personal friend of Hundertwasser. The book is midi size (about 8" x 10", and there are about 200 color reproductions of selected paintings, architectural works, photos of the artist, and more.(Too bad there's no discounted Volume II, which is a Catalogue Raisonné of Hundertwasser's entire painted oeuvre.)
Unfortunately, it looks like this "25" edition has recently gone out of print. I hope I'm wrong, but Taschan doesn't list it on its website anymore, only the 200-page book by Harry Rand (which I also own, and which is also very nice.) So if you like Hundertwasser, this is a book to look for now, while copies are still available.