WP-Print
Displays a printable version of your WordPress blog's post/page.
Florian 'fkrauthan' Krauthan
wp-mpdf
Print Wordpress posts as PDF. Optional with Geshi highlighting.
Erick Hitter, Steven K Word, and Oomph, Inc.
WP Print Friendly
Extends WordPress' template system to support printer-friendly templates. Works with permalink structures to support nice URLs.