I have a number of O’Reilly books myself and I must admit, when their spines are all nicely lined up, they look awesome on my bookshelf.
They are now running a promotion that allows you to download an electronic version of any of the paper books that you own for only $4.99 each.
I will almost always want to own the paper version of these books, but having a portable version that is searchable makes access to the information I need extremely convenient.
Promotion ends at the end of October, so...