Linux Mint is the usual recommendation. If you've used Ubuntu for a long time most things should be the same only with a far more polished UI (in my opinion). Its the distro that many old Ubuntu users moved to after the Unity release.
You can grab it with MATE, Cinnamon, KDE or Xfce. I personally use MATE or Cinnamon most the time, but you can check out the individual projects to see which interface you like more.
http://www.linuxmint.com/download.php
If you're really brave and want to mess around (and have time to kill) ArchLinux is a lot of fun and has a lot of documentation but its also a lot of work.