I made eight dives with Poseidon, which is a PADI dive centre. Two dives cost 130 000 pesos (July 2007) and in that price all the equipment is included. The dives are made by boat and in-between them there is a short break at a shore were you will get some snacks (small sandwich, biscuits and coke). There is no toilet anywhere. Three days we used the big boat with roof, which is good for protection from the sun. One day we were using a smaller, open boat and I thought I was not going to like it. But it was fine. It was quite cloudy that day and we were not so many divers and there were no loud music so we could speak to each other.
When I was in Taganga they were building a pool at the dive centre. So Poseidon will be the only dive centre with a pool were you can do different exercises during the courses.
The diving is good in Taganga. There are many corals, both soft and hard. Other things you will see during the dives are: lots of tube worms, fire worms, big angelfish, green morays and smaller spotted morays, cowfish, octopus, parrotfish, spotted drum, barracuda, lobsters and many more.
Uppdate August 2008: I made only two dives this year as I was just passing by. The price was lower than the prvious year, 120 000 pesos for two dives (maybe it depends on the season). There were a lot of divers and most of them took different courses. All groups were small and I was happy to dive alone with a dive master. The owner Max took a look at the places I had been to the previous year and we went to two for me new places. That was great!
The place is perfect for many things. Especially diving. I got my first PADI diving licence uin Taganga. There are several dive shops with friendly and helpful instructors and nice people. Most of the dive shops are located along the main street which runs along the beach. One of the cheapes places is Ser Buzo, which also has an amazingly nice and fun staff. They also give you lodging for free if you take a dive course with them. The dive sites are also amazing. Most of the dive shops have their own small cabins somewhere on the coast where they take you between dives for lunch. The atmosphare is amazing and the people are great.
Equipment: All of the scuba equipment comes with the course. If you have your own, you can just borrow a tank or have it filled and use the dive shop for taking you to the best locations.
There are several providers in the area. Felipe recommends one of them (forgot their name, but it's ran by 3 assosiates, one of them, Roberto, is French). The prices are dirt cheap. The courses cost you around $140 USD and typically include a couple of free dives after the mandatory ones or accomodation in Sta. Marta.
Equipment: Best to rent equipment here. I paid $133 USD for 2 free open-water dives plus the advance open-water PADI certification course (5 dives, including a night dive).