The good thing about diving in Curaçao is that you don't need a boat. You can rent a car, put your equipment in the back and drive to one of the many beaches. You can buy a guide in a local bookshop, e.g. the "Complete guide to landside diving and snorkeling locations in Curaçao". The local Drive and Dive road map shows all diving spots too. A very good overview is also given on shorediving.com.

Probably the most spectacular site on the island is the wreck of the Superior Producer. You can swim in and around the ship, visit the cargo area and the steering hut. In good conditions you can see the length of the ship. Too bad that it lies in about 30 m deep water, so your time is limited. On rough days this can be a tricky dive, with currents and big waves.
You can visit this site from the shore, but many dive operators offer boat dives as well.

Another small wreck is the tugboat. It lies in 3m deep water, so it's good for snorkeling as well. In most books and on older maps, this location is pointed out as a boat dive. That is because Caracasbaai peninsula was closed to the public. However, now that Caracasbaai peninsula is open for everybody, you can reach this wreck from the shore as well. From the tugboat you reach the spectacular wall of Director's Bay in minutes, so this place is definitely a must for divers too.

To be honest: there are no bad dive sites on the island. Everytime I go to another spot, I think "wow, this is fantastic". There was one exception: the entrance to Piscadera bay was the only disappointing dive site I've seen so far.

There are many dive shops on the island. A lot of the shops are connected to a hotel, (often too expensive) but there are others as well. I have very good experiences with Atlantis Diving , Silent Immersion and Safe Diving. Not only do they have all the usual courses, but they also arrange trips for certified divers. Very handy if you are on your own, or if you don't have a car. Safe Diving also offers boat trips to the few spots that are not accessible by car. One of these spots is Mushroom Forrest, a really good dive. At the beginning of this dive you also vistit the Blue Room, the only small underwater cave you can visit.
Wederfoort (a.k.a. SAMI Divers) in Boca San Michiel is good for taking a course (and they are beautifully located on the waterfront), but they don't seem to offer regular trips for other divers.

In November 1999 Curaçao suffered from the tail of hurricane Lenny. In some shallow parts 80-90% of the coral was destroyed. This is especially true on Banda Abou (the west side of the island). However, on Banda Ariba (the east side) things are not so bad. Also, the coral below 10 m is still very good. Fish is still abundant everywhere.

Be sure to check out Reef Care Curaçao before you go and learn more about protecting the reef.