Tanzania has two noncharter airlines, Air Tanzania and Precision Air, operating domestic flights. Service on both has improved recently, though don't arrive at the airport expecting timeliness. Charter airlines are another option: Prices are manageable if you can get a group together large enough to fill the plane (usually three- or five-seaters). The two train lines in Tanzania, the Tanzanian Railway Corporation's Central Line and the more comfy and efficient TAZARA line, link Dar es Salaam with various destinations.
Buses travel by day throughout Tanzania - they are not permitted to travel at night (though some do). Be aware that road accidents are probably the biggest safety risks while travelling here, as roads are poor and buses can be very speedy. On the northern routes (Dar es Salaam to Moshi and Arusha), Fresh ya Shamba is one of the better lines. On the southern routes (Dar es Salaam to Iringa and Mbeya), go for Scandinavian. For shorter trips off the beaten track, mini-buses (also called dalla-dallas) are an option.
You might minimise the risks of the road by driving your own vehicle, though for most trips outside major towns you will need a 4WD. You can rent a car at one of the many agencies in Dar es Salaam. A fair number of travellers cover at least some of the country on their bicycles. Main roads are generally not good for this, though many secondary roads are ideal - as long as you stay ultra-alert.
If roads aren't your thing, you can hop onto a ferry on Lake Victoria, Lake Tanganyika, Lake Nyasa and along the coast. Sailing a dhow, a boat that has been on the coastal waters for centuries, seems a more romantic experience, but the journeys can be long and uncomfortable. After several accidents involving tourists, the government has prohibited foreigners on nonmotorised dhows, or on any dhow between Dar es Salaam and Unguja. Despite the efforts and risks involved, however, sailing under the moonlight with the breeze in your hair can be a great way to travel.