Devel::Peek lets you do this. From the pod:

    use Devel::Peek;
    $a = 42;
    Dump $a;

    The output: 

    SV = IV(0xbc818)
    REFCNT = 1
    FLAGS = (IOK,pIOK)
    IV = 42
[download]

The PVIV, IV, RV and other types are explained in perlguts.

For anyone who is interested, there is a good explanation in the Internal Variables section of Simon Cozens Perl 5 Internals.

--
John.