I must be the last one to spot this. But I couldn't find a link in the search.
www.scribd.com has some scanned in books on japanese (I found some genki, minna, kanji and grammar books - but not tonnes of stuff)
Plus google books has tonnes of scanned in books (not whole book) inc RTK II (new version) and quite a few others. There are quite a few Japanese (language - not text) books too.
There was someone asking about books to read and wanted to know if the book they wanted to buy was too hard. Sorry I forget what the name of that person was. But might be worth a look on there? You can do an advance search and change the language options.

Some of the google ones seem have tonnes of the book in there. Certainly worth a look if you want to be more selective in your book buying.

amber