It's easily Bali's most visited diving site, and with good reason. Tulamben sports not only a fantastic wreck dive, but also an excellent wall dive. The black sandy bottom coupled with the wide variety of marine life makes this a very popular place for underwater photographers.
Although there are close to 20 dive sites in the immediate area, there are two in particular that draw the most people: The USAT Liberty shipwreck and the Wall. I've covered those two in more detail here. The others include Kubu, just north of Tulamben, and Batu Kelebit, just to the south.
Tulamben has a small group of dedicated dive resorts to choose from, but truth be told it's a rather isolated and undeveloped area. You might want to spend a few days here to see some of the other dive sites - and see the main dive sites before the vans from the south show up - but you probably wouldn't want to base yourself here for a long stay.