Check package version using apt-get/aptitude?

apt-get

You can run a simulation to see what would happen if you upgrade/install a package:

apt-get -s install <package>

To see all possible upgrades, run a upgrade in verbose mode and (to be safe) with simulation, press n to cancel:

apt-get -V -s upgrade

apt-cache

The option policy can show the installed and the remote version (install candidate) of a package.

apt-cache policy <package>

apt-show-versions

If installed, shows version information about one or more packages:

apt-show-versions <package>

Passing the -u switch with or without a package name will only show upgradeable packages.

aptitude

The console GUI of aptitude can display upgradeable packages with new versions. Open the menu 'Upgradable Packages'. Pressing v on a package will show more detailed version information.

Or on the command-line:

aptitude versions <package>

Passing -V will show detailed information about versions, again to be safe with the simulation switch:

aptitude -V -s install <package>

Substituting install <package> with upgrade will show the versions from all upgradeable packages.

Another way using dpkg and grep:

dpkg -s <package> | grep Version

Another option, if you don't know the full name of the package, is formatting aptitude's search output:

aptitude search <package> -F "%c %p %d %V"

%c = status (package installed or not)
%p = package's name
%d = package's description
%V = available package's version

Reference: http://linux.die.net/man/8/aptitude