I maintain a file of headhunters that I have come in contact with. If I lose my job (or even feel like I'm going to), I've got about 10 people who can earn money by finding me my next job.
Its definitely good to keep in touch with a list of people like this. I think you'd be better off to ask your friends for recommended people. Most recruiters that randomly contact you are crap.
Alternatively compose a "Thanks, not now" template that you send to all recruiters when they email. Then later on hit them with a "How about now?"