Trashmail.net went pay-only (because of spammer abuse!) last summer, and I only discovered it recently as I don’t use these services all that much. During the search for alternatives, I found new ways to search for alternatives.
The service AlternativeTo has always been a good place to go for desktop software alternatives; now they include mobile platforms and online applications as well. The list of alternatives to TrashMail is extensive and interesting.
The other interesting item is Google’s related: operator. This can be used during searches, but at the bottom of a search there may be a link to sites similar to the one searched for. In the case of Trashmail.net, Google returns a lot of alternatives.
As an ironic twist, consider this: Google has a list of sites similar to AlternativesTo.net.