It should be in the repositories soon: plexmediaserver EDIT: it is in the repo now.
It will only be available for armv5 as it only comes in binary form and is not available for other architectires. Please don't ask!
For rasbperry PI you will need to use armv5 rootfs (not available for download, but can be created. Raspberry pi kernel and firmware for armv5 is in the repos).