List of available ubuntu packages for ARM processors?

Check out http://ports.ubuntu.com/ubuntu-ports/dists/<release>/main/binary-<architecture>/Packages.bz2 (there're different architectures for ARM - armhf, arm64, armel, etc. - and not all might be available for every release, focus on the LTS releases, see https://wiki.ubuntu.com/ARM for further infos), e.g. http://ports.ubuntu.com/ubuntu-ports/dists/trusty/main/binary-armhf/Packages.bz2. You'll find a list of packages which are available through apt-get if you add

deb http://ports.ubuntu.com/ubuntu-ports <release> main

to your /etc/apt/sources.list. The list isn't in handy format, but decompressing and opening it with a text editor and using its search function will help.