MailChimp has two methods. They have something called Inbox Inspector (powered by Litmus) that can both show you visuals of your e-mail in various clients but also has about 10 different spam filters to test against. They also have something called "Delivery Doctor" which does a quicker check but is more a safety valve than anything super useful.
More generally, http://emailsuccess.com/ is a new service that you can send your e-mail to and it'll produce a report on all the problems, both technical and content-wise. I only just tried it for the first time and it gave a great report.
There's also http://spamcheck.postmarkapp.com/ which is a JSON-accessible API to which you can send a mail and it'll run checks. Alternatively, you can just paste your message into the page.
More generally, http://emailsuccess.com/ is a new service that you can send your e-mail to and it'll produce a report on all the problems, both technical and content-wise. I only just tried it for the first time and it gave a great report.
There's also http://spamcheck.postmarkapp.com/ which is a JSON-accessible API to which you can send a mail and it'll run checks. Alternatively, you can just paste your message into the page.