in reply to cpan modules - pm only?

If you look at the author's page on CPAN, you'll see a list of Registered Modules for that author (see here for an example).

The codes after each module name indicate whether the module uses a combination of C and Perl (look for the 'c' flag) - for example, DBD::Sybase has flags of RcmOp.

More information on these flags is here.

I don't know if all modules on CPAN have these flags associated with them, though, so this may or may not help you :)