http://www.gamedesign.net/node/46?PHPSESSID=426efd1bd701f030e82f5620d8084b6cThe URL above explains the trigger_push entity's undocumented "angles" key.
trigger_push has a documented "angle" key that takes one value, the direction you wish to push.
But the coders left another key in there and didn't tell anybody!
That key is "angles" with an "s".
It's value is "yaw pitch roll".
So if you want to push a player at a 30 degrees angles up, and directly to the east you would add this to your trigger_push entity: "angles -30 0 0".
Remember up is negative on the first value.
Roll has no effect so always make it 0.
Read up and have fun pushing things around.