There are quite a few temporary and anonymous email options out there to help you skip the spam and still register for sites, but Mailnesia differentiates itself by automatically clicking registration links for you and supporting HTML.
You don't have to register for it, just type whatever name you'd like followed by "@mailnesia.com" and you'll be on your way. Unlike many temporary email services, Mailnesia supports most common email types, including HTML and MIME, which is handy if you're getting download links. It also allows you to generate a RSS feed for the email box so you can keep tabs on it if you want. The automatic registration clicking works as advertised and on most sites you can simply reload the page after a couple seconds and find Mailnesia has already taken care of the confirmation. Of course, you don't want to use this for anything involving private information, but it's handy for trials and downloads.