Here is a huge (really huge!!) list of flash games for download.
You can see this :"Index of /games" in its title.
It is basically a listing of folder containing flash files (swf files) from the server.

http://games.lynms.edu.hk/games/

This is one more collection. It is small one but has a good collection.

http://tinyurl.com/yp6mq6

This is not yet blocked in websense under games category.
So you can also use it at office for timepass ;)
(Thanks ryankendall)

Here are some more downloadable games.
Enjoy!!