We currently offer a massive range of downloads for FSX, as well as older flight simulator add-ons for the ever-popular FS2004, FS2002, CFS3 and now becoming ever popular with dediced virtual aviators is Laminar Research's X-Plane series.
This is basically a crash, without the fire, smoke, twisted aluminum and death, which flight simulator x left out for tact. In most cases your approach speed is too low, which means your rate of decent was too fast. Basically, the plane was dropping out of the air rather than gliding to a touchdown. If you check the kneeboard in each aircraft, in the 2d (F10) cockpit -- the checkmark -- each aircraft should have a landing speed table. I usually go with a middle of the table speed rather than trying to figure out what the plane is going to weigh at landing. For instance, if you keep the Boeing 737 between 145-155 knots, you shouldnt sink into the runway unless you are causing the rapid decent (nose down).