Graham Barr announced
Documentation pages on search.cpan.org now contain a list of related modules. For an example see LWP::UserAgent
This list is determined by data created by Perlmonks.org about which modules are discussed together.
Where's that data search.cpan is pulling? How do we contribute to it? Some of the modules listed in SEE ALSO sections of the documentation are immediate candidates for these links.
Update: as pointed by Corion, that information is probably being extracted from cpan module search with a XML display type and filling up the field module and selecting "Other Modules". That information is automated, relating the appearance of modules referenced in the same article. This automation is good because it is automatically maintained, but it is dull sometimes relating, for example, LWP::UserAgent and Data::Dumper.