One year and counting!
Asking what to do in LA is like asking what to do in any of the world's largest cities - except everything is spread out and you must drive! So, rather than trying to hit everything (which will be impossible due to traffic), try and find a few things near one another and get to know one part of the city. Or just spend the whole day at the beach!
Since I've already been asked where the closest In N Out to the hotel is, let's get this one out of the way. To get your California fast food burger fix, go east on Ventura Blvd for about 5 minutes. The In N Out is on the right hand side of the street, between Winnetka Ave and Corbin Avenue.
August should be hot in LA. Which means great beach weather!! LA has some beautiful beaches, and many are fairly close to where you'll be staying. The closest one is Topanga Beach. If you want to go a little further afield to a beach in Malibu (which is still relatively close), try Zuma Beach or El Matador State Beach.
Finally, if you want to combine some beaching with other LA activities, go to a beach in Santa Monica or Venice. It won't be quite as nice from a pure beach perspective, but you can combine it with a trip to the Santa Monica Pier, 3rd Street Promenade, Venice Boardwalk, or Venice Canals.
There are a myriad of cultural activities you could take in while in LA, so these are just the highlights. If you like museums, the Getty Center Museum is not only a great museum, but it also has nice gardens and grounds with fantastic views of LA (on a clear day). If you want to hit a lot of museums at once, check out the Miracle Mile, which has many museums, as well as good restaurants and other fun stuff.
If you like modern architecture, the Frank Gehry-designed Walt Disney Concert Hall in downtown LA (conveniently near the equally beautiful modern Cathedral of our Lady of the Angels) is an absolute must.
If you want to walk around fun/fancy neighborhoods, try Hollywood (where you'll find the Hollywood Walk of Fame and Grauman's Chinese Theater), Beverly Hills (where you'll find Rodeo Drive), Westwood (which is adjacent to UCLA and near the Getty Center), or even Downtown LA (which is where the Walt Disney Concert Hall and LA Cathedral are located).
Finally, if you're a space geek (and we all know there are bound to be some of those at the wedding), the Griffith Park Observatory has been recently renovated and is supposed to be pretty cool. You can also go hiking in nearby Griffith Park.
Which brings us to our last subject. The coastal mountains that separate the Valley from the beaches have a ton of hiking trails - many with views of either the Valley or the coastline. Very close to the hotel, you can pick up Valley views by hiking at the top of Reseda Ave. If you'd prefer views of the ocean, check out Temescal Canyon. These two are really only the beginning of a whole host of great outdoor activities.