One of the big confusions for those who are interested in trying Linux is that there is no main version, like there is for Microsoft Windows or Mac. In fact, all Linux really is, is the kernel, the underlying part of any operating system. What makes up a certain Linux system, be it Damn Small or Ubuntu, is all the other stuff: specific tweaks to the kernel, utilities, window management applications, hardware drivers, etc. This collection of programs and settings is called a distribution. So, were do you get these Linux distributions?
One place you can always find downloads is the distribution's website. If you already know the name of what you want to try, Google it for their website. The website should have download links to the CD or DVD images. Some popular ones are: Ubuntu, OpenSUSE, Fedora, Debian, Puppy, Mandriva, Damn Small Linux, and Linux Mint.
There are also many sites that review and post articles about various Linux systems. One popular one is Linux.com. Another is Distrowatch, a database of distributions along with news, reviews, and how-to articles. Distrowatch also has a nice list of the pros and cons of the most popular distributions.
Online Lists of Distributions
Here are some lists and searches for Linux distributions and software:
CD and DVD images of Linux distributions can sometimes be quite large. Even with a fast Internet connection these can take hours to download. With a slow connection, downloading a DVD image may take a day or more. Torrents are a download protocol, often called file-sharing or peer-to-peer, that enables downloads to be much faster. You'll first need a file-sharing client. One simple one for Windows is uTorrent which requires no installation. If you have a DSL router, you may have to forward a port for the client. See Port Forward for a wealth of instructions on many types of routers.
Once you have the client set-up, you'll need to find the torrents. For Linux downloads, the most popular is Linuxtracker. Another one with distributions is Linux 23. Be aware that torrent sites may have copyrighted downloads that other users have illegally uploaded. I've never seen any on Linuxtracker, but Linux23 did have some copied Microsoft downloads.
Linux Magazines and Books
Often, print magazines and books will include a CD or DVD with distributions and other software for readers to try out. Some magazines include Linux Pro and Linux Journal. Two how-two guides that cover popular distributions are A Practical Guide to Ubuntu Linux and Fedora 9 and Red Hat Enterprise Linux Bible. How-to books such as the O'Reilly Linux series and the For Dummies Linux series may also include CDs. Any large bookstore such as Barnes & Noble, Borders, or Amazon should carry these titles and more. Keep in mind that these will be cutting edge when first published, but with books especially, if it sits on the shelf for a while, the software maybe out of date.
As you can see, Linux is actually easier to find than those other operating systems. It also comes in a wonderful variety for every type of computer user. Since most distributions are free and easy to find, why not try out a few to find the one that works best for you!