Can anyone recommend a good maintenance-free rear shock? The old shock just gave up its life in my old single-pivot all-mountain frame. I'd like to replace it with something tough and maintenance-free, so that I don't have to worry about air pressure, oil leaks and other things to check before I ride. It should also be mud-proof as much as possible. Weight, price, performance and all others are secondary. Does anybody have a good recommendation? 160 or 165 mm length.

Also, is there more than one standard of mounting rear shocks? I vaguely remember some sort of ball joints being promoted for this a few years ago, but I don't know if this caught.
All shocks require a little bit of love from time to time. A coil rear shock will require less maintenance than an air shock. The simpler the shock, the less maintenance you will need to do. I have only ridden fox in the back, but have never had any issues. I would recommend looking at the Fox Van R Coil. The Rock Shox Vivid would also work really well.

If you want to be able to pedal well, you should look at the higher end coils that have propedal, or airshocks.