I have a Sony Alpha 100 and I've bought an adapter M42 for it. I'd like to know, which lenses can I use on my Sony?
The Sony A100 will work natively with all Sony A-mount lenses, as well as the older Minolta AF lenses (some of which are excellent).
As for m42 lenses, there are tons of those, from various manufacturers. Some are very nice and others are dogs. All will be manual focus of course, and the aperture you will have to control manually on the lens as well.