I always use screen and I use pbcopy/pbpaste all the time. What about them doesn't work?

You've made me second guess myself. I was getting bit by this bug http://trac.macports.org/ticket/18235. It does not persist any more. Apologies.

my latest nifty screen trick (borrowed from a similar variant for xclip) goes:

    bindkey -m > eval "stuff ' '" writebuf "exec sh -c 'pbcopy < /tmp/screen-exchange'"

then when you've made a selection in screen Copy Mode, just terminate it with '>' to stick it onto the system paste buffer.