Ubuntu Linux is an absolutely awesome Linux distribution that is fairly easy to use, and just works. I've used _tons_ of distros, and I'll save you a lot of time and headaches by just recommending you to try Ubuntu if you want to try Linux. It has a lot of the same features as other distros, but distributions always have the odd thing that's broken in them, or there's no packages available for them, or some other weird problems. I was a die-hard Mandrake (8.1 to 2005 LE) user for 4 years, but I also tried other distributions during that time. I've used Knoppix, MEPIS, Yoper, Fedora Core 1, 2, and 4, SAM Linux, and a bunch of other little distros, and they all work fine for a couple of weeks, but eventually you'll realize the achilles heel of each, and switch to another distro. I was floored when I tried Ubuntu. Why? I've found very few bugs in the OS (no critical ones) after using it for 3 months straight, there are packages for every piece of software you'd ever want, it never has any weird problems the other distributions have, and best of all there's tons of documentation and a huge community.
Here's a few links to get you started: http://distrowatch.com/ Check out the right-hand side of the page to see Ubuntu's page hit ranking - this is a pretty good indication of the popularity of a distro, people vote with their feet.
http://www.ubuntu.com The official Ubuntu website.
http://www.ubuntuguide.org/ The unofficial Ubuntu guide - This answers every question you'll ever need (the "How to add extra repositories?" part is especially useful), it shows you how to install new applications (take a look, it's super easy)
http:///www.ubuntuforums.org The official Ubuntu forums, another great resource (very very popular)
Personally, Ubuntu absolutely destroys Debian and Fedora. Debian doesn't get updated nearly enough, and is a hard distro to master. They don't ship the stable version with current software, you'll waste a lot of time with Debian. Fedora is pretty good, but FC4 had some quirks. It doesn't come with out of the box MP3 support, it had some weird bugs for me, and it comes with GCC 4.0 (breaks compiling with some programs, more needless headaches). There was just a couple of annoying broken things in Fedora too (my Palm pilot wouldn't work with Evolution because of some stupid bug.) The nice part about Ubuntu is that if you have any questions or think you've found a bug, just look them up in the guide for a fix, or search the forums, it's super easy.
Anyways, enough Ubuntu promotion (I just want to get you off on the right foot with Linux, a crappy distribution can make your life a living hell, especially for a newbie).
-Albert Santoni [firstname.lastname@example.org]