One alternative to normal 35mm format lens, is C-Mount Television lens. These lenses are usually pretty cheap, but they also have very small image circle, not to mention the normally abysmal resolving power. You can usually find very wide angle C-Mount TV lenses as wide a 6mm. Unfortunately, all you would usually get is a small circle of an image with a huge black border. In other words, not really usable. There are some that covers a larger sensor, such as the 1 inch sensors. You can tell by the size of the lens. If it's really small, it would have a rather small imaging circle. A friend of mine showed me a trick to check the approximate image circle of a lens. Find a light source, and use the lens to form the clear image on your palm. The size of the image gives you some idea how much coverage the lens can provide.
I came across a Cosmicar 12.5mm f1.4 TV lens. Cosmicar is a division of Pentax that manufacture close circuit TV lenses. The size of this lens is almost the same as the Angenieux 70mm f2.5. It's very fast for such a wide angle lens with a maximum aperture of f1.2. Mounted on the G1, the equivalent focal length is 25mm. This is wide enough for most occasions. BUT, you don't get the whole image, sad to say. This lens would cover a one inch sensor, but not enough to cover the Micro 4/3 sensor, hence its heavy vignetting. As with most wide angle TV/Cine lenses, the edges are blurry. This particular lens would still give you usable image if cropped at the long edges.
In terms of image quality, contrast is low wide open, with a soft glow, but still quite sharp. From f2.8, center sharpness is actually quite respectable with markedly improved contrast. Resolving power seems low, as expected from a TV lens. Not too crazy about the colour that comes out of this lens either. The colour seems washed out. Minimum focusing distance is 0.3 meters, or about 12 inches.
The 14-45mm kit lens is still light years better than this cosmicar lens in terms of sharpness, contrast and colour saturation, but it does free you from Photoshopping your own vignettes. In some situations, this lens gives you somewhat unique characteristics not possible with the kit lens, especially in dim lighting condition where you can take pictures at f1.4. It's kind of fun to play with, as long as you can get it cheap.
Wide Open at f1.4 -- note the soft glow effect and heavy vignetting
Fence -- Aperture is around f4. Note drab colour.