Ubuntu's newest release (6.06 LTS) will be released on June 1; unfortunately, I'll be on the road then, so won't be able to download it until I get back in a few weeks. This release is a landmark for Ubuntu, as it is planned to be supported for five years, even though newer releases are going to be released at six-month intervals.
Ubuntu is a popular1 Linux distribution that is intended to be extremely easy for novices to use. Ubuntu is based on Debian (the Linux distribution I currently use), and since my trial run of Ubuntu back in March was mostly problem free, I'm extremely tempted to switch. Ubuntu has a LiveCD that you can download (from here), burn to a CD, and then try out on your computer without actually installing anything onto your computer (I've written more about that here). If you've been wanting to see what using Linux is like, Ubuntu's LiveCD is a great way to do it.
1 - Ubuntu was ranked 1st in the "Favorite Distribution" category of Linux Journal's 2005 Readers' Choice Awards.