Panasonic L1 has a Four Thirds lens mount and currently there are 47 native lenses available for this mount.
The latest released lenses that are compatible with the L1 are the Venus 33mm F0.95 CF APO, the Samyang 135mm F2.0 ED UMC and the Samyang 300mm f6.3.
Panasonic L1 doesn't have a sensor based image stabilization system but
3 of these lenses already comes with optical image stabilization.
Since Panasonic L1 has a Four Thirds sensor, it has a focal length multiplier of 2× 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 L1.
You may also also be interested in these:
Panasonic L1 Lenses with Image Stabilization
Panasonic L1 Lenses with Weather Sealings