Yesterday saw the first beta release of the new PostgreSQL version 9.4. Along with the sources, we uploaded binary packages to Debian experimental and apt.postgresql.org, so there's now packages ready to be tested on Debian wheezy, squeeze, testing/unstable, and Ubuntu trusty, saucy, precise, and lucid.
If you are using one of the release distributions of Debian or Ubuntu, add this to your /etc/apt/sources.list.d/pgdg.list to have 9.4 available:
deb http://apt.postgresql.org/pub/repos/apt/ codename-pgdg main 9.4
On Debian jessie and sid, install the packages from experimental.