How many of you know who owns an image once you take it? I think its pretty simple, if you take it you own it unless you have made other arrangements.
If someone pays you to photograph and turn over all the files you are pretty much giving up all the rights to the those images. If a band asks you to come shoot their show regardless of being paid or not you OWN all the rights to those images unless you tell them they can have the rights.
It is good practice to make sure that all your agreements are written and not just verbal. I like to write a simple e mail describing exactly what I am doing and exactly what the client gets.
For example, I will be photographing xyz and delivering you images that can only be used online. If you would like to use them for any other purpose please contact me to discuss usage fees.
Or I will photograph xyz and you have the rights to do anything you would like with the images.
To me it comes back to you own everything you take unless you give up your rights.