If you were to sell t-shirts with movie quotes on them, how would you
go about licensing the quotes? Are they trademarked?

You may potentially run afoul of both trademark and copyright law,
depending on what quotes you use.  For example, let's assume that you
want to print, "Go Ahead--Make My Day" on a t-shirt.  First, you would
need to make sure that this was a fair use under copyright law since
even though you are only using one sentence, the owners of the
copyright to that particular Dirty Harry movie might object.  Assuming
you cross that hurdle, then you would need to make sure that the
phrases you select are not claimed as trademarks by anyone else--you
can perform searches at
http://tess2.uspto.gov/bin/gate.exe?f=tess&state=6lagc2.1.1.  Just
because a phrase does not show up at the PTO site, however,  does not
mean someone doesn?t claim TM rights in it.  I would probably contact
the movie studios that distributed the films from which you wish to
take quotes and ask about taking a license under both copyrights and
trademarks for purposes of making t-shirts--that's the safest course.

Keep in mind Mel Gibson was collecting licensing fees for people
selling "nail" necklaces for a tie-in to his movie "Passion of the
Christ."

Surely the Bible is public domain by now, isn't it?