Pentax K100D has a Pentax KAF lens mount and currently there are 163 native lenses available for this mount.
The latest released lenses that are compatible with the K100D are the Carl Zeiss Makro-Planar T2/50, the Samsung D-Xenon 16-45mm F4 and the Samsung D-Xenon 18-55mm F3.5-5.6.
K100D also has a sensor based image stabilization system which means that all of these lenses will be stabilized when used on the K100D.
Since Pentax K100D has a APS-C sensor, it has a focal length multiplier of 1.5� so you have to multiply lenses original focal length with this multiplier to find the Full Frame equivalent focal length of the lens when mounted on K100D.
You may also also be interested in these:
Pentax K100D Lenses with Image Stabilization
Pentax K100D Lenses with Weather Sealings