We, at Retrocade.net are looking for level developers!
People interesting in making quality levels for our games are to mail us at email@example.com.
Right now we are primarily looking for people capable of creating whole levelsets (20-40 levels). If you can make quality levels of that number you won't go unpaid. How much you can get will be individually discussed per game per person per amount of levels you make.
People who only want to make single levels are also encouraged to participate. For those we can offer mention in credits or, if levels are really good, one-time payments.
More details in the official news post.