In the case you did not see it yet, published 6 free sIBL/ HDR sets that are freely downloadable:
First 5 sIBL sets are ideal for WIP renders of character models.
those can be downloaded in the link below:
one free Dutch Skies 360 sIBL set can be downloaded in the link below
(note this Dutch Skies 360 is downloadable until 1 juli 2011!)