I find it hard to find titles, even working titles, for my novels. Two out of the three novels I'm written/writing are unnamed. I've only found a name for my third novel recently.
To find a title, I take a mental look at my novel. What is the main theme? If I can't derive a title from there, (which I find I don't) I take a look at some of the major events that happen in the book. What happens that is extremely important that has a huge impact on the end of the book? This is pretty much where I found my title for the third novel I have.
Now, to find titles for the other two.