Ubuntu 12.10 Quantal Quetzal is here (x86)

You can download it from here.

Ubuntu 12.04 LTS Precise Pangolin is here (x86)

You can download it from here.

Ubuntu 11.10 Oneiric Ocelot is here (x86)

You can download it from here.

Ubuntu 11.04 Natty Narwhal is here.

You can download the image here.