Motorsport.com looks like a great source of pics. They are a reasonable resolution (480x720) and the watermark isn't in the way. Here is some of their pics of the ING Grid Girls from this years Melbourne F1.
Another round of the V8s, another great gallery over at Inetpics.com. It looks like being a good source of pics all year long so make sure you go check it out after every round. Here is some highlights (I am lovin those Jim Beam Girls):