I'm a big believer in having a great title. I think it can help you focus your ideas and get your one-sentence pitch right from the very beginning. Yes, the title will likely change if you should be so lucky as to have your work published. But if you can come up with something catchy; a great phrase to sell your idea and concept straight away, then the rest should (hopefully) be easy. Or easier, anyway.
For my current novel, I originally had the title The Ex Factor. I thought it was great (and I still think it is!) but a search on Amazon revealed the title had already been taken. D'oh! Second try came up with The Hating Game -- a play on The Dating Game and rolling in the vengeful attitudes of the exes my protagonist will encounter.
How do you come up with a title? Do you leave it to the end, or is the title the first thing that comes to mind?