To study or reference inscriptions of various places in Karnataka, you can down load EpigraphiaCarnatica volumes from here.
Another link from where you can download all volumes of EpigraphiaCarnatica.
Good resource to get information about important places in each district of Karnataka.
Kannada Sahithya Parishath
Many rare books published in the last century have been digitized and available in PDF Format here
The library at Mythic Society at Bengaluru is a treasure trove of books. Some of them are available in digitized format here