L.A. is expensive right now for a lot of reasons. It’s always been relatively expensive to live here, so factor that in. Second, when the housing market collapsed, a lot of people who had to leave their homes or postpone plans to buy one stayed put in their apartments or had to move into apartments. Combine this with a paucity of affordable housing being built (most of what’s going up right now are condos for moneyed people, and buildings being overhauled and refurbished for the same crowd of moneyed people), and apartment buildings that were under under rent control being torn down to make room for new condos for the well-heeled crowd (see above for more on this), and it adds up to a very tight rental market right now. “Affordable areas” are slowly becoming less affordable, and desirable areas are becoming more expensive, and rents are rising across the board.
Silver Lake is a gentrified part of town popular with gays and hipsters right now. Expect to pay a premium for a decent place. Echo Park is slowly gentrifying, but it can be sketchy (I wouldn’t say it’s “gangland central’; it’s a lot safer than it used to be).
The Valley is cheaper, and North Hollywood is actually fairly decent (It’s only “on the fringe” in the northern/western parts); it’s a wee bit pricey because of proximity to what passes for the arts/theater district on Lankershim, plus the metro stop (also on Lankershim).
Hard to say, really, what would be a good fit for you without knowing more information, such as how much rent you can afford, and what your priorities are. Generally, the closer to the mountains and the ocean you are, the more expensive it will get. The farther you are from mountains and ocean, the more affordable it will get (but it also means you are more likely to be close to/in sketchier areas).
Good luck.