I'd like to share to all Renderosity members my hdri maps, created in different places and lightning conditions. They are 5000 x 2.500 (lat/long) format and can be used in your private or commercial projects, however to get them you'll need to register as a client with valid email (sorry for that but I just wanted to reduce bandwidth usage).
If you want to convert it to mirror ball format you can use free software called Luminance HDR. And if you need background you can create it from hdri with free Picturenaut.