There is really nothing notable in Chinatown these days. In the San Gabriel Valley, try NBC in Monterey Park on Garvey (just south of Atlantic): the seafood is fresh, plentiful, and very fast. We always go for crab or lobster in either a ginger and scallion sauce or a black bean sauce. The salt baked prawns (actually deep fried and then sauteed, with flecks of chile fused onto the paper thin shell) is not bad (although the former Harbour Village -- now partnered with Empress Pavillion from Chinatown, also in Monterey Park on Garvey, although on the northwest corner of Atlantic -- has a better version of this dish: plumper, and slightly less greasy.) NBC also has good steamed fish: go with the tilapia (called lu yu in Mandarin), or the rock fish. Whatever you do, no matter what anyone says, SKIP OCEAN STAR (also on Garvey, in Monterey Park, just north of the former Harbor); it's strictly for lao wai ("foreigners," i.e., whites). Very limited menu, cooked for Western tastes.
I think there's a few places left in CHinatown worth going to for seafood - and sea cucumber.
NBC seafood is excellent, but there's the rival network CBS seafood in LA Chinatown that's worth a visit. I'm just kidding, you won't find Les Moonves peeling shrimp in the kitchen, but you will find extremely fresh and resonably priced seafood.
They have the usual stuff there - dungeness, maine lobsters, but they also have the crystal crabs from Australia and great sea cucumbers. I went there last week and had a very satisfying dish of fresh conch with yellow chives. It was such great value at $11 - best conch I've had anywhere. I've also had their sea cucumber which is great.
I also like Ocean Seafood, NOT OCEAN STAR which I think is overrated. Ocean Seafood has excellent and fresh seafood all the time. They have extremely large tanks with a large variety of fresh fish, clams, crabs & lobsters and fresh shrimps....(not that the size of one's tank should ever determine one's character...)
And their dim sum rocks.
There's a Korean/Chinese restaurant in K-town on Olympic and WEST of Vermont. It's called Young Kim and they serve the most comforting bowl of spicy seafood noodle soup. First off, the noodles are REALLY good, springy stuff that you'd want to eat yards of. The broth is perfectly spiced and there's plenty of shrimp and sea cucumber to make you happy.
There's also the Korean version of the Chinese "jia jang mien". I don't know what its called in English, but growing up, we called it "chinese spaghetti" (allright Chowhounds who know, don't get your panties in a knot...just share the English name of this if have the info). But Jia Jiang Mien is a noodle dish with a dense sauce of soy bean paste, lean pork, squash, and other goodies. It's ladled onto noodles and mix as you like.
Oh, and the Young Kim chicken - deep fried and surprisingly greaseless chicken legs (just the meaty part, bone cut away), then stir fried in a sauce with peas and onions. Sounds gross, but it's really addictive.