It Never Rains in Southrn California, doesn’t mention LA, but it’s clearly about it.
Nobody’s mentioned the Doors -* L.A. Woman*?
Warren Haynes has a song called Angel City which I’ve always taken to be about L.A. (but i could be wrong)
“Guess the angel I had on my shoulder
Stayed back in my hometown
And here in Angel City
There just ain’t enough angels to go around”
Drinking in L.A. - Bran Van 3000
White Punks on Dope - The Tubes
Born in East L.A. - Cheech Marin
Coming into Los Angeles – Arlo Guthrie
“Welcome to the boomtown” David and David… is soo 80’s LA…
Anything by The Fifth Dimension or The Association… they were LA acts featuring the Wrecking Crew…
“A long December” By Counting Crows…
one more day up in the canyon… and one more day in Hollywood…
How about Zappa’s Valley Girl? I think the San Fernando Valley could be considered a part of the greater Los Angeles area, no?
There’s also “Tinseltown Rebellion.” And probably scads of others.
“Los Angeles, I’m Yours” by the Decemberists is not exactly a love letter, either.
Some more: “L.A. Freeway,” Guy Clark. “History Lesson, Part 2,” The Minutemen (“We learned punk rock in Hollywood / drove up from Pedro…”), all of Chavez Ravine by Ry Cooder, “Celluloid Heroes,” The Kinks.
Hollywood Nights by Bob Seger
Beverly Hills by Weezer
Pico & Sepulveda!!!
Also, The Four Preps’ 26 Miles (Santa Catalina).
This was the first one that came to my mind. 
Los Angeles is Burning - Bad Religion
“I’m considering a move to LA” by Art Brut
A song I listened to a couple of times recently before I decided I don’t like it is set in LA. Garrison Starr “Beautiful in Los Angeles”.
“Los Angeles I’m Yours” by the Decemberists
(when moving here I timed the cd just right so the song started as I was cresting over I-5 and could see the city in the distance.
I thought of a whole list when I read the OP… By the time I got through all the responses I was left with Lullabye by Shawn Mullins.
I’ll try to think of some more.
Oh durrr.
California Love by Tupac Shakur.
Madonna - ‘Hollywood’
In The Staples Center, during their sports games, they play this I Love L.A. song that’s kind of catchy and inspiring. I don’t know what it’s exactly called or who sings it though. Anyone have an idea of what song I’m talking about?
Also, I guess it could possibly not be set in Los Angeles. The singer could sing about L.A. while he’s in a bus in New York. 
America: Ventura Highway
Darn you, Maggie!
I’m one-upping with a video (I’m trusting Google because I can’t watch YouTube here)…Pico & Sepulveda.