I'm assuming you means stuff you could do in a day trip driving out of Santiago.
Los Molles is about 2.5 hours drive north of Santiago and is beautiful. I haven't dove there yet, but I know Molles well since I used to go there for work about once a month. There's a LDS in Santiago and one of the guys that run it owns a small op on the beach there with gear and a compressor. I've seen some of his pics and I can't wait to get in there.
I've also heard quite a bit about another place a bit south of there called Papudo (still probably about 2 hours from Santiago) and know a couple of ops that work out of there. I don't know if they have compressors there or just bring tanks from Santiago, but wither way, it's on my list of places to give a try.
Other than that, small ops are few and far between. If you rent gear in Santiago, you could go to Punta de Tralca, it's only an hour and a half from Santiago straight out to the coast, and is one of my favorite spots. The north side of the point is very protected from pretty much all swells, except the rare ones that come out of the north, in which case you just dive the south side of the point.
Don't forget that the central coast of Chile is very comparable to the central-northern coast of California. If you're bringing gear, make sure to pack a cold water suit.
When are you coming? I live about 15 minutes from Punta de Tralca. If you give me some notice I may be able to meet up with you.