|Search for Chromium in Software Center|
|Chromium 15 from the official repositories|
The latest stable build can be installed from the stable PPA. It's been a while since Ubuntu 11.10 was released, so there should be a newer build available already but that doesn't seem to be the case at this time.
Adding the PPA would get you the latest stable build once it's available, so it's still okay to add it if you want to stay on top of things.
~$ sudo add-apt-repository ppa:chromium-daily/stable
~$ sudo apt-get update
~$ sudo apt-get install chromium-browser
Installing other Chromium builds
If you prefer a more cutting edge version of Chromium, there's always the Beta, Dev and Daily channels. Simply use the appropriate PPA line with add-apt-repository command and install/upgrade chromium-browser accordingly.
Links to the various Chromium PPAs are available on Launchpad.