i would say definitely get the chax plugin for ichat, i really like the log viewer to look at old conversations in ichat.
handbrake for sure
i however, have to disagree on the quicksilver. i had it and i never found it very helpful. it could be that i was just not using it correctly but i really think if you have your computer set up the way you like it you can find an access the things you need much faster than quicksilver can. i never thought it was very good