Debian is the only 'real' Linux-distro, as in 'everything in here is free like the kernel'.
Pros: Xtremely good support, and the way you update the distro (apt-get) is really great.
Cons: Lacks support for some of the newest hardware.
Choose this distro if you want to learn Linux!!
Redhat is the closest you get to a desktop looking like Windows out of the box.
The distro in itself is good, and lots of hardware/software- solutions get certified for this distro. It got certified by the Pentagon earlier today actually...
Redhat has an upgrade-option that looks a bit like the one in WindowsXP.
Suse is the European counter-part of Redhat, based out of Germany. They have many nice solutions if you want to migrate from a Windows environment for your whole company... Hence, they're a bit business-minded.
Then there is Mandrake, which is French and regarded as the 'living on the edge' distro, as it has the newest software, newest apps and has most hardware-support. Even if it can be a bit buggy...
Anything else is for people with special interests if you ask me...
A word of advice:
Don't install more stuff than you need, and stay away from the KDE-desktop. ;-)
Good luck and have fun!!
