Version 1.14 – OLD stable version

sudo apt-get install -y pgadmin3

1.18 and latest version

The latest version is available from the pgadmin git server.
Only disadvantage: it has to be build from scatch. Depending on your machine capabilities, this can take several minutes.

# Prepare
sudo apt-get install -y build-essential automake libwxgtk2.8-dev libwxgtk2.8-dbg libxml2-dev libxslt-dev

# Add Postgres Repository

sudo sh -c 'echo "deb http://apt.postgresql.org/pub/repos/apt/ wheezy-pgdg main 9.3" > /etc/apt/sources.list.d/postgresql.list'
sudo apt-key adv --recv-keys --keyserver keyserver.ubuntu.com 7FCC7D46ACCC4CF8
sudo apt-get update
sudo apt-get install -y postgresql-server-dev-9.3

mkdir -p ~/build/pgadmin3
cd ~/build/pgadmin3
git clone git://git.postgresql.org/git/pgadmin3.git
cd pgadmin3
bash bootstrap
./configure
make
sudo make install

Troublshooting

Error:
bootstrap: line 38: aclocal: command not found

Fix:
sudo apt-get install -y automake

Error:
configure: error: could not find a suitable C++ compiler to build pgAdmin
Fix:
sudo apt-get install -y build-essential
=> install g++ compiler

Error:
configure: error: Could not find your PostgreSQL installation. You might need to use the --with-pgsql=DIR configure option
Fix:

#Postgresql
#http://wiki.postgresql.org/wiki/Apt/FAQ
Error:
W: GPG error: http://apt.postgresql.org wheezy-pgdg Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 7FCC7D46ACCC4CF8
Fix
sudo apt-key adv --recv-keys --keyserver keyserver.ubuntu.com 7FCC7D46ACCC4CF8

Error:
configure: error: Could not find your wxWidgets installation. You might need to use the --with-wx=DIR configure option
Fix:
sudo apt-get install -y libwxgtk2.8-dev libwxgtk2.8-dbg

Error:
configure: error: Could not find your libxml2 installation. You might need to use the --with-libxml2=DIR configure option
Fix:
sudo apt-get install -y libxml2-dev

Error:
configure: error: Could not find your libxslt installation. You might need to use the --with-libxslt=DIR configure option
Fix:
sudo apt-get install -y libxslt-dev

References

1. Postgresql FAQ
2. Aclocal Command Not Found