indirect: Lexically warn about using the indirect object syntax. This module seems very useful for catching difficult to find bugs. This blog post gives a compelling case for its use.

namespace::autoclean: Keep imports and functions out of your namespace.

namespace::clean: Keep imports and functions out of your namespace. Allows a bit more control as compared to namespace::autoclean.

Carp::POE: Carp adapted for use with POE. May be interesting.

Module::CoreList: Generate lists of core modules shipped with Perl. This module is maintained by the Perl 5 Porters. I can see this being useful for package dependency generation.