http://www.solspace.com/software/detail/related_entries/

Solpace’s related entry module might be a very good upgrade, replacing the current system of “inspired by” dropdown list that has grown to almost unmanageable scrolling length.

Con:  Nearly $70.

Pro:  Ease of use.  Multiply related entries possible.

Con:  Will it be compatible with EE2.0?

Unanswered Question: Is it able to relate entries from other weblogs?  If it is, this would be a very big plus.