aftercolumbia's Lander spreadsheet at http://spreadsheets.google.com/pub?key=pPW38BHXYUTlDPPe3cNIcPw
A lander vehicle has many of the same components as a space vehicle with several important additions:
2) Landing "radar". It may not be actual radar, but something needs to measure the distance from the surface and lateral velocity to execute a landing maneuver. additionally, some vehicles may be performing orbital rendezvous and the equipment may be asked to assist in these mission phases. Notional concepts include Radar, Lidar, Parallax, Video, UWB, Magnetics and other sensors.
3) Cargo and deployment. Most landers are built like a truck, it carries something and has a way of discharging its payload. Typical devices may include ramps, doors, cranes, tiedowns, latches, hardpoints, and more.
4) Advanced Propulsion. a lander probably needs the ability to vary the amount of thrust its engines are producing. Additionally, since a positive thrust to weight (not mass just weight) ratio is generally required, the engines need to be sized larger than on a simple spacecraft.
5) Translational Maneuvering. Landers and rendezvousing spacecraft need the ability to translate in all three axis relative to a target. A simple spacecraft need to hold an attitude, but a lander needs to be able to stop lateral translations for final approach. Typical solutions are the ability to lean on the main engines (lean over the engines to translate the lander) and/or small auxiliary engines. (similar to RCS engines, always for prox ops.