HDR Files for download

Liking this program, simple and easy to use. I figure once i can get the handle on this i can maybe progress to a full blown render program unless the AO program improves in the near future. However, i am a new user and just trying the trial Pro package, can you provide some recommended sites that have some good HDR files i could grab? As well, when i tested one of the environments, the building was floating above the ground plane, even though i have it drawn on the axis. Is there anyway to move the environment up or down or do i have to manipulate the object?

HDR Heaven is a great source of free HDRIs.
The position of the environment is determined by the direction the camera is looking, but you can rotate the environment around the vertical axis by going to Environment->Rotation