"EASY" ones that are designed specificly for desktop systems are Redhat, Mandrake, and SuSE. Redhat is the most popular distro out there, so that would be a good one to start out with.
You can download ISO's free from links provided by linuxiso.org, however depending on the Distro you decide to try out first you should go to their websites and read thru some docs. Redhat has some decent installation manuals and such.
Other ones such as debian or slackware are designed for more experianced users and manuals and stuff for them are geared towards people who are already somewhat familar with Linux/Unix operating systems. However that doesn't mean that they are bad choices or anything, it just means that you will have to work harder and be willing to get frustrated for a while until it all begins to sink in.
There are also dozens and dozens of other distros out their designed for specific purposes. There are many University-based distros designed for student learning, Multimedia specific distros like
Evil Entity Linux (never tried it myself

).
There are also language specific distros, with the biggest example of Conectiva (from brazil, geared for spanish/portagese speakers).
Most people will try out several distros until they settle on one that matches their disposition.