If you sign up for the free trial at VideoBlocks and then quit, they will offer you a yearly price option – I will be doing that at the end of this month. Other good sources of RF footage (I use them all) are Pond5, Footage Firm (and their StockFootageForFree.com) and Digital Juice’s VideoTraxx.
As for attribution, none is required. The clips are yours to use as you see fit.
