We used Green Footprints, a company based in Arusha, for our Tanzania trip this past October. They were fantastic, and really catered to us. We were a family with 4 adults and 5 children. They responded to all of our emails, planned fantastic adventures, from night game drives, canoeing, bike rides, etc.. We loved our guides, they were personable, wonderful and easily went with the flow of dealing with 5 children. And no, I don't work for them, just would highly reccomend them. Our tour contact, Mirjam actually met us a couple of times on our trip to make sure everything was going smoothly.

I forgot to say that GF was also reasonably priced. For about 2 weeks, we stayed in very nice smaller accomodations, went to a fly in camp, and 2 zanzibar, with airfare from San Francisco, about 4500. If you want more details I'd be happy to respond.