Modern Perl assumes you're already decent at programming,
so it elides some basic stuff in favor of explaining how
Perl works from philosophy to programming in the large.
Learning Perl assumes you've never programmed before,
so it spends more time on the basics, covers less of the language,
and doesn't explore the philosophy of Perl in as much detail.
-- chromatic (author of Modern Perl) comments on the philosophy behind his book
Since you've already read Learning Perl,
I suggest reading Modern Perl next.
Modern Perl is free and very quick to read.
If you have more time, and want to get inside the head of
the language designer,
is also good.
As for good "second" books on Perl, these are both good:
For a comprehensive list of nodes that discuss Perl books see: