The most important thing to mention here is Project Gutenberg. There you will find a huge collection of not-any-more copyrighted works that have been digitallized by volunteers.
To read I prefer a printed book but for reference and searching for quotes it is quite useful.
A list containing some of my books, mainly for my reference but if you're interested...
Apart from that I can offer my advice on what to read:
| The Bible | - | Various Authors |
| Confessiones | - | Augustinus |
| Faust I | - | Johann Wolfgang Goethe |
| The Hitchhikers Guide To The Galaxy | - | Douglas Adams |
| Hamlet | - | Shakespeare |
| A Man's Approach to God | - | Richard Rohr |
| Waiting for Godot | - | Samuel Beckett |
| The Screwtape Letters | - | C. S. Lewis |
| Aus dem Leben eines Taugenichts | - | Joseph von Eichendorff |
If you actually want to read one my advice is to go to your local bookshop and there browse a little more you might get interested...