http://www.ubuntu.com/
Ubuntu is probably one of the better newbie distros out there for free.
Plus you can use Gnome, KDE, XFCE or any other Window Manager
you want.
I keep Ubuntu around for testing myself.
http://www.xandros.com/
If you don't mind paying some money, then I recommend Xandros if
you're just coming from the Windows world. It's setup is even easier
than Ubuntu. And it's setup to mimic Windows rather well, making the
switch from Windows to Linux clean and easy. If you get the premium
edition then you get CrossOver Office which is a modified Wine, which
allows you to run quite a lot of Windows program from Linux. Xandros
is a bit strict though with respect to letting users just install anything.
Xandros uses only KDE for it's Window Manager.
I run Xandros Desktop 4 / Home Edition - Premium on three of my
computers here. The Wife's computer, and the house computer that
everyone else uses. Then I dual boot my laptop with XP and Xandros.
Personally, I was tired of the "Linux Distro Game" and went with what
I felt best suited my needs and my expectations. Xandros was the one
that covered just about everything I needed and expected.
You'll have to ask yourself some questions about what you want out of
a Linux and what you expect. Then check out the most common or
most known Linux distros, read up on them and see which one sounds
like it fits your list.
Trust me, you don't want to get into the game of trying every freaking
distro out there and switching from one to another everytime a new
distro pops up. I played that stupid game for a few years and wasted
a lot of time.
You can visit
http://www.distrowatch.com/ to find out the latest distros
and read up on them.
-Garrett