DPKG
apt-cache
dselect - text-based apt-like program
aptitude - CLI & text-based apt-like program
aptitude install pkg
aptitude remove pkg = install pkg-
aptitude autoclean (or clean - all packages, not only N/A)
aptitude search
aptitude update - updates package cache
aptitude full-upgrade (or safe-upgrade)
synaptic - GUI-based Software Manager
dpkg-reconfigure