I am a freelance PJ. One of the more widely used kits for PJ is a 16-35 and a 70-200, for crop bodies such as the ones you have it is almost the standard kit. Since you said you want to go wider, go with the 16-35 either new or old version. If you're serious about getting a lens that will last and you wont have buyer's remorse, get a 2.8 version. If you were using a mark III you could go with the 17-40 due to being able to shoot at ISO 3200 and 6400, but with your bodies stick with the 2.8 lenses. I have a mark III and I sitll wouldn't want the f/4 version anyway.
Also, don't go with primes, its too impractical out in the field. Foot zooming doesn't work when your back is up against a wall. I only use mine (a 50 and 85) when I specifically know what to expect on a particular assignment and these lenses will help my photos. Since you already have a 50, you can grab it when you think the light might suck and when using a flash is going to be a problem.
I carry a 1.4TC with me on every assignment in case I need some extra reach for my 70-200. It has saved me quite a few times, and my back by not having to carry my 300 f/2.8.
As for the flash, I would get a 580 due to being able to put it in manual mode. (Assuming the 430ex you mentioned can't do this) In addtion, please get an off camera shoe cord. You won't use this all the time, but it is helpful to get rid of that 'blasted' flash look and red eye. (this takes practice though as you will be holding your camera with only 1 hand and the flash is the other)
If you have any questions, please feel free to PM me. My portfolio can be seen at www.erictom.net, so you can get an idea if you think I know what I'm talking about or not.