[Picture from wikipedia.org]
This wreckage is located in Coire Mhic Fhearchair, a corrie of the 1010m munro Beinn Eighe in Torridon, and lies directly below the Triple Buttress, one of the most famed pieces of mountain scenery in Scotland. It requires a three-hour walk from the main road through Torridon. Several large pieces of the Lancaster are observable, including one of the wheels, which I took a picture of in August 2002.
There are some good pictures of this site on the TFDACSS website here, the ACSS site here and the SAWS website here.
Update Nov 2007: Apparently a gully in the Triple Buttress is well-known to climbers and contains some of the wreckage, including a propellor jammed into the rocks that is used as an anchor point!. The gully is even called 'Fuselage Gully' by climbers. There's a great photo of the wreckage in the gully on UKClimbing.com here (registration required to see full-size image).
Update May 2009: The propellor mentioned above made the BBC news! See here.