We ran into some pretty bad traffic, which was annoying, but once we got to Alki we found an amazing parking spot, loaded up our stuff and staked out a spot on Alki Beach. Alki (way on the South end of Seattle) is famous for it's actual sand and it's view of the Seattle skyline. It's also the only beach in the area where you're allowed a fire. Because of these factors, it's also extremely crowded and very touristy. There are a ton of little shops and restaurants around.
Overall, Alki was a pretty fun trip and I'd be happy to do it again, especially if we had a bit longer and got there earlier. That said, Discovery Park is still my favorite beach in Seattle.