Juergen Kreileder over at blog.blackdown.de has a really nice step by step howto on how to enable SSL (HTTPS) for a WordPress blog.

This article does assume that your running Debian Sarge with Apache 2. This should work for Ubuntu as well.

We have received some feedback asking us to add an HTTPS howto into the WordPress whitepaper, however, it is difficult to provide a detailed howto with so many OS and web server types and implementations. With this said, perhaps a more generic section can be added in a future release.