A lot of people use gmail.com (from google) or live.com (from microsoft, the start is https://mail.live.com/?rru=home&livecom=1), not only for temporary, but also as permanent addresses. You might see the occasional ad they use to offer it free to you, but if that isn't an objection, use one of the two.
I am placing an item on Craigslist and I am a little leery of using my real email address. Which temporary email service could I use? Preferably free.