I've only just started this library and there is lots more to come, so follow me on twitter for updates:
This work is licensed under a Creative Commons Attribution 3.0 Unported License.
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You may also like these other Royalty free paid for clips on iStockPhoto.com:
View Dramatic clouds with sun rays stock footage clip at iStockPhoto.com
View Dramatic Timelapse Sunset Rays stock footage clip at iStockPhoto.com