Panasonic GF1 has a Micro Four Thirds lens mount and currently there are 125 native lenses available for this mount.
The latest released lenses that are compatible with the GF1 are the Rokinon 7.5mm f3.5 Fisheye, the Samyang 7.5mm F3.5 Fisheye MFT and the OM SYSTEM 9-18mm f4.0-5.6 II.
Panasonic GF1 doesn't have a sensor based image stabilization system but
37 of these lenses already comes with optical image stabilization.
Since Panasonic GF1 has a Four Thirds sensor, it has a focal length multiplier of 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 GF1.
You may also also be interested in these:
Panasonic GF1 Lenses with Image Stabilization
Panasonic GF1 Lenses with Weather Sealings