Easiest that I know of is
Knoppix.
It doesnt really install, You can boot right off the CD and it acutally gets to the desktop in less than 2 minutes without putting anything on the harddrive, along with a usuable offfice app and 1.7GB of accessable programs (Dont ask me how they do it). This is good if you just want to see what Linux feels like and work in it a little bit to see if its something you want to go on with. Its fully functional, and actually has the nicest GUI that I know of right after install, but since its CD and RAMdrive based, you cant save any configurations to keep at a following reboot. It picked up my mouse, keyboard, network, power management, video card, sound, wireless, and just about anything I can think off on my laptop without any intervention from me. It even mounts all your windows drives automatically, no matter the file system. Its a great option for anyone just getting started.
For an actual installation of Linux, I recently came upon SuSE 9.0. I've only tried this and Mandrake, and prefer the SuSE installer and OS a lot more. You can either purchase this at the store (Pro = $70, Personal = $40, I hear they come with excellent reference books that are worth the price alone), or do what I did, and do an FTP install of it. You download a 20MB iso, burn that to a CD, boot with it, pick what you want from the installer and itll download just those components, straight off thier FTP without any intervention from the user. I believe that the FTP install is configurable up to the professional edition of SuSE retail, minus a few non-open source apps. Full detailed instructions can be found
here. Its a little slow to boot, maybe because I picked too many components, but otherwise, I really like SuSE 9.0. Its the first Linux that really impressed me (Before I discovered Knoppix) and has a home on my harddrive.