You're asking for a list of third-party plugins and other modules dynamically or conditionally used by commonly-used modules. A lot of modules have these. In fact, most large distributions probably do it.

Here's a few I've had to deal with:

• DBI uses database drivers (DBD::*).
• JSON uses JSON::PP or JSON::XS.
• LWP uses protocols (usually LWP::Protocol::*).
• syntax uses features (Syntax::Feature::*).
• XML::SAX uses of many SAX-based XML parsers.
• XML::Simple uses XML::Parser or XML::SAX.