Personally, I'm a huge fan of Hannah Montanna Linux.
http://hannahmontana.sourceforge.net/

OK

Slackware - Reminds me of the good old days when Linux was SIMPLE. Isn't that the reason everyone switched to Linux??? Because under the hood it was simple and easy to understand compared to Windows. Now there's all this COMPLEXITY and I hate it! I'd switch to a BSD if my 420 Linux games worked...

I also like appliance/Just Enough distros that make you forget your computer is a computer so:

OpenELEC - Media player
Lakka - Retro game console
OpenWRT - Router (Configuration is nicely abstracted through UCI system. opkg pkg manager. It's really great!!)
SteamOS - Valve has been slacking IMO, they left BPM untouched for a long time then started improving it just weeks before Steam Machines released. It is not there yet but it will get there I still beleev

Other/Cool/Unique:
NixOS - You write a config file describing a system and it will build it for you. Atomic updates/rollbacks. Upgrading is the same as doing clean install so you never get any cruft! It's really sick!
Bedrock Linux - Minimal distro with set of tools for managing a bunch of chroots and having it all look like one system. So you can e.g. mix packages from Debian and stuff from Gentoo's portage, or any other distro. It's really sick!!

Steev, what do u think of arch?