Helloooooooooooooo!
Was just sticking my head in when I noticed this thread and I thought Id give you some info...
While LA is not on my list for best party towns in the US, mostly due to California's ridiculous 2am alcohol law, there are still some decent choices depending on what you are into.
Venice - has a very laid back international crowd. Most of the places are restaurants that move their tables and open outdoor smoking areas and has a very loungey and relaxed feel.
Westside/Santa Monica - More of your sportsbar and fratboy type places. Usually easy on the wallet and not difficult to get into. Good for a last minute outing.
Hollywood - If you are in a decent sized group, want to spend a good amount of money for bottle service, and are looking for a bit younger of a crowd with your typical night out there are many places here for you to go. There are smaller more intimate places as well, and in the past couple years places like Hemingway's and Supper club have opened with live music and a more 28-35 age group.
Silver Lake - If live music and a more bohemian crowd are your thing, Silver lake is a great place to go. Lots of artists and liberal students live and party in silver lake.
Downtown - Happy Hours (5-8 weekday) There are great places like Edison's but only during these hours when professionals are out drinking before they go home. Afterwards or on weekends, it pretty much turns into an extension of Hollywood.
Hotel scene - Standard, W, Roosevelt, Viceroy, are places where you can go and get bottle service or a room, and the night scene is usually half decent.
So while LA isnt Miami or New York, does have that ridiculous 2am last call, there are things you can do, but I would probably start planning early and decide how much you are willing to spend, because LA is spread out and traveling between destinations can ruin your night... As others have mentioned Vegas and even SF are decent alternatives, but I would go to them as well, not completely replace LA with them...