The best fast food burgers in the US (IMHO) however, are from In-n Out Burger - there are branches all over LA - they are only in CA. They are a family owned chain, - everything made fresh, to order, really small menu just burgers, fries and shakes. They even cut the fries by hand from real potatoes - you can see them doing it in the kitchen!
Check out their website
http://www.in-n-out.com for locations, but the closest to DL is on Brookhurst.
The secret is to ask them to "animalise" your burger - or fries - this means they put a whole lot of melted cheese and fried onions on it - soooo good!
It's kind of a badly-kept locals secret - it's not on the menu but everyone asks for it. Try it!
mmmm dreaming of an in-n out burger right now.....