Just buy a domain. (Score 4, Insightful)

I have my own domain and I can create an unlimited number of throwaway addresses. If they behave, I keep it active. If it starts getting spam, I know which business I can't trust and I direct it to /dev/null/

For example, if I were to register with slashdot, I could just use [e-mail]

I can keep it around for as short or as long as I want.