I guess I have to go with "other" too. I don't seem to have a consistent method of finding books for my "wish list" - which I then track until the price comes down.
Various methods I've used in the recent past:
- book reviews in "non-traditional" sources (like The Economist, Guardian Weekly)
- short and long lists for Man Booker Prize, Orange Prize, and sometimes even the Pulitzer Prize winners
- interesting author appearing on The Daily Show or sometimes even on France24 in English
- interesting sounding book that has been made into a film (I usually prefer the book over the film anyhow)
- scanning various categories on Kobo or Sony store sites