There are a lot of yellow dresses and clothes on Gossip Girl. I liked Jenny's little yellow satin bubble dress in the "Dare Devil" / Sleepover episode. Here are some cheaper alternates, in case you wanna knock off the look:
Gossip Girl Dresses: Yellow Gowns for Ball and Prom
Hollywood Life Gossip Girl Photo Spread, Oct 2007
Gossip Girl: Serena's Jeweled Black Dress in Episode "Dare Devil"