I like SpringImages.com and not just because I am the kind of nerd who will use it. Even without paying a subscription you get pretty broad usage terms:
If you are a Registered and a Subscribed User, you may
* Download or create printouts of certain Content under certain restrictions and conditions. All reproduction and distribution of such printouts, and all downloading and electronic storage of materials retrieved through the Content shall be for your own internal, personal or scholarly use.
There is much more detail about the site here! In terms of what most casual users would need, this certainly hits the spot. Opening up these images is a very smart move and one that should be pretty widely welcomed. This is exactly the kind of material it is hard to find in the real world of web search which is the real value of opening up the database for searches even if the results of those searches might yield unusable images (for subscription reasons). I wonder how well the site plays with Google?
Go have a look!