I use 33mail.com for the same purpose - it gives you a unique wildcard subdomain (and also a shortened domain (<yoursub>.33m.co) so you can create uinque addresses per signup etc, without the problems of + being rejected (or gicing away your real email address)

You can then block any address with a click if it's being abused.

If you're feeling generous, enough people using this link will earn me premium features: http://www.33mail.com/rj37w3