In addition to the places people have already recommended, I would suggest you check out
Big Lou's Toys and
Blast From The Past.
Big Lou's has a huge vintage selection, but also carries some Sideshow - especially Star Wars Premium Format. They sell a lot of stuff for people on consignment so the selection is always changing. Blast From The Past has the largest selection of Sideshow stuff I've ever seen in a brick and mortar store. Very friendly and helpful staff. I was going to pass on a lot of the Star Wars 1/6 figures but saw them in person here and knew I had to get them.
Oh, I will also recommend
Meltdown Comics, especially when you are looking for comics. They have a large selection of trades and a ton of Japanese Toys and Manga.
Enjoy your time in L.A.!!!!