Just a quick point, keep your objectives simple. If you set up a scenario where very intricate objectives are required, people are going to forget about them, get confused and wind up being frustrated.
Simple doesn't mean boring. Scenarios don't have to be dirt simple like "downed pilot" or "get this container from point A to B". Throw in several containers, make them locked, spread out the keys, or even give the keys to the other team. My favourite scenario involves chess clocks located at several points on the field. Each of the two sides gets a colour and has to keep their colour on the chess clocks running for as much as possible. This one is just like a real life capture and hold from the Battlefield video games.
There's lots out there. Look around and modify as required. Rinse, repeat.
"Anyone with a name like Amanishourbariki should give a few letters to the poor Ng family." - Snarfangel, Fark.com