Jeff Merkley's current address can be found at http://www.leg.state.or.us/house/hsedem.htm, where there is an email link. Since he is Speaker of the Oregon House until he goes to the U.S. Senate in January, you can send mail to him while the Oregon legislature is still in session:
Session Address:
Jeff Merkley
900 Court St. NE, 269
Salem, OR 97301
Session Phone:503-986-1200
rep.jeffmerkley@state.or.us