Easter Island is definitely where to go diving in Chile.
The thing about diving continental Chile is it's a lot like California, but without the kelp. You're in luck though, since most of the dive operations that I know of are based in Santiago and do most of their diving within a two hour drive from there.
The two places that I would recommend diving are Los Molles and Quintay. Both are small, isolated fishing/vacation towns near high biological productivity (upwelling) centers with biological diversity and diving conditions as good as it'll get in the region. Quintay's a good bit closer than Molles (only about an hour from Santiago on the highway to Valparaiso whereas Molles is right about a two hour drive north of Santiago. I think there's another op in Papudo, along the coast about half way between the two, near a sea lion & penguin colony, but I'd have to dig them up. Plus sea lions & penguins are all over the place.
Los Molles is the furthest of the three, but it's isolation is kind of it's charm. The town is very small, but since you'd be there in the high season it will be pumping. It is catered to by ScubaChile (
Academia de Buceo Scuba Chile). These guys actually have some pretty cool videos of what you can expect to see there and in central chile on their website. They were trying to establish a marine reserve there, but I haven't heard anything new of it lately.
Quintay is probably a safer bet than molles. First of all it's a lot closer, but also it's a rather sheltered cove that doesn't get hit my the wind and swell as much as Molles resulting on more diveable days. Plus there are at least a old whaling wreck or two within recreational limits that they guys can take you to (the town used to be based around whaling back in the day and the old processing plant is now a museum). Also it was one of the first locally managed fisheries in Chile, so even the fishermen understand a bit about conservation. There are two op's in Quintay: Austral Divers (
Austral Divers) and Buceo Quintay
BUCEO QUINTAY - BIENVENIDO .
I don't have any experience with any of them, other than trying to find a wetsuit which none of them were able to help me with (I'm 6'4" in a land of midgets). I've seen all the op's from the outside and met some of the guys in person and they all seem to be on the level. They're all trying hard to promote diving and make a buck at it in their own way.
Let me know if you need anything else. Good luck and have a great trip. I hope you're planning on going to the torres del paine and perrito moreno. SO WORTH IT!!!!!!