Hard question since there are soo many. But I'd say either www.shockwave.com or www.miniclip.com

NewGrounds also has a lot of flash stuff, especially flash movies

But some of them may not be appropriate for the work area so read the warnings, if there are any. Actually I think NewGrounds would be the best out of all of them, since it has the most content. The videos vary from comedy to some serious topics, so you should find something of interest, the games as well. Most are violent though.