In this post you will find top cheat sheets for Ubuntu which contain quick reference for Linux terminal commands (Ubuntu is Linux distribution so almost every core Linux command is applicable also to Ubuntu). If you have some more Ubuntu cheat sheets and wish to share them — just leave a link to it in your comment (thanks!).
Ubuntu Reference by FOSSwire
This Ubuntu cheat sheet is based on original FOSSwire Linux Ref you may also find useful. Ubuntu Reference is also available in editable ODT file (opens with openoffice.org Ubuntu default office suite). Links to localized versions of this Ubuntu cheatsheet are available here.
Debian/Ubuntu Reference Card
Ubuntu is based on Debian Linux distribution so reference card for Debian is also applicable to Ubuntu. Links to localized versions of this cheat sheet including Russian, Japanese, Hindy translated PDFs are available here.
Linux Cheat Sheets