It all depends on what you’re willing to spend. Pond5 is fine but is at the lower end of the price spectrum (I have some clips out there myself).
Also at the free/cheap side is Footage Firm (http://www.footagefirm.com/free-footage.html) and their sister site Stock Footage for Free (http://stockfootageforfree.com). Considering what you’re paying, their stuff is quite good (I have used many of their clips in my work).
On the higher end are places like Artbeats (http://www.artbeats.com) which has great video but you’re gonna pay a lot for it. They do have freebie downloads of clips if you sign up.
Somewhere in the middle are libraries like Digital Juice’s VideoTraxx HD (http://www.digitaljuice.com). They are only selling their HD collection right now but occasionally bring back limited runs of their older VideoTraxx 1, 2 & 3 libraries (SD) for about $100 each.
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