Sometimes a website can be a real eye opener and that is what happened to me when I first visited DiscoverTanzania.org
I never knew how beautiful the country is (you can really tell from the great pictures) and got all the information needed about the climate, medical advice, visa information and even what to wear!
Needless to say that there is a separate section for pretty much every location including safari destinations and packaged holidays. There is also comprehensive information on accommodation and tours across Tanzania.
Strongly suggest you to have a look at Tanzania and Zanzibar but also visit the Mikumi National Park and Stone Town in the Zanzibar section.