Still pictures give a more detail view of what is occurring at at one point of time, while Video Cameras do a better job of giving an overall picture of what is going on (Thus both compliment each other).
I have always said protesters should be organized in groups of 20 (Roughly the size of a a Classic Platoon, now since WWI the Platoon has grown to over 40 men, the pre-WWI platoon was 20), with 1 of the Platoon with a Video Camera and 1 with a Still Camera (With today's digital Cameras this can be done by one camera). For example Kodak P850 and P712, are both 12 x Lens and have video capability. In addition, if the platoon can afford it, a good SLR. The SLR Digital should have a 80-200 Zoom Lens, Cost about $2500, and a Video Camera of about the same price. These Cameras are expensive so often best to be purchased by a larger group than the Platoon, but if the decision is made by the Platoon to buy such a SLR and Video Equipment each member of the platoon is only spending a total of $200 instead of $5000.
You should also be willing to donate money for even better equipment further up the "chain of Command" (I.e. to groups of "Platoons" formed in groups of 100, the pre-WWI number of men in a Company. A SLR with a 600 mm lens with a low f values and internal stabilization cost several thousand EACH, thus the price is best spread over a lot of people for example if 100 people would donate $100 each you have $10,000 to spend on a lens and Camera Combination.
One last comment, I would stay with Canon, it is the most used SLR in the USA today, Nikon is the better known name and produces better lens, but the difference is so small given how these cameras are going to be used Canon is more than good enough (Also go with the Highest Mega-pexils you can, but at least a 5.0).
At the same time you are setting up the above hierarchy of film taking, you should encourage people to have their own digital cameras (You can get some pocket ones for around $100, to take pictures missed by the better cameras).
Some suggestions:
The new P712 by Kodak, not a true SLR (The lens are NOT Changeable) but a good picture with a 12 X mega-pexils optical Zoom lens, price is $499.00. The P850 is almost as good but only has 5.0 Digital. These are good for use by the 20, but you should look at better equipment (But better than nothing and if someone destroys your $500 Kodak, it hurts a lot less than a $2500 SLR).
http://www.bhphotovideo.com/bnh/controller/home?O=productlist&A=details&Q=&sku=441485&is=REG&addedTroughType=categoryNavigationA Canon SLR with a 80-200 is what you should opt for, if you can, A EOS 2.0 costs $989.99 at B&H
http://www.bhphotovideo.com/bnh/controller/home?O=productlist&A=details&Q=&sku=348299&is=REG&addedTroughType=categoryNavigation70-200 Zoom (The largest you can use and still be hand-carried): Price: $1249.99 at B&H: If you want something bigger remember anything bigger will have to have a tripod or at least a mono-pod, thus better further back away from the main action.
http://www.bhphotovideo.com/bnh/controller/home?O=productlist&A=details&Q=&sku=457678&is=USA&addedTroughType=categoryNavigationHere is a 600mm lens at $7199.99: Notice this is NOT a Zoom, it is a fixed 600 mm (about a 12 x like the Kodak P712, but with a much lower f value AND a larger picture, over all a MUCH better lens)
http://www.bhphotovideo.com/bnh/controller/home?O=productlist&A=details&Q=&sku=186153&is=USA&addedTroughType=categoryNavigationYou need the SLRs at least at the 100 person level, just to have the best pictures available as to what happened. At the 20 person level the Camera should be it the rear unless it is recording something.
Video Cameras with zoom lens:
Canon: (Price: $2249,95)
http://www.bhphotovideo.com/bnh/controller/home?O=productlist&A=details&Q=&sku=264368&is=GREY&addedTroughType=categoryNavigationA Digital Camera for the Individual (Price $89.99):