Found some awesome free large HDRI's (100Mpix)
http://www.weiss-ag.info/gallerie/hdr-einzelbilder-shop/
You will need to click on the title of every HDRI to download it. (for example, for the first one, click on the orange/red "Messpaar mit Targets")
Some do cost money, but only if you want to use these HDRI's without copyright.
So these are actually free as well (as long as you give them some credit)
Beware, they are very big! the downloads are 600mb each. Inside you will find 2 exr's. One is called "****tiled.exr"
this one you want to delete.
cant get them to work