Entrepreneurs: Adam Goldstein, 23; Steve Huffman, 27

Funding: $5.2 million from investors, including Y Combinator, Ignition Partners, and SV Angel

Adam Goldstein and Steve Huffman entered the market for online-airfare sales in August with Hipmunk, a search engine that weeds out long trips and out-of-the-way connections, ranking results based on convenience. Goldstein is a recent Massachusetts Institute of Technology graduate and Huffman previously co-founded social news site Reddit.

Wisest funding decision: Taking seed money from Y Combinator. "They're the Harvard or MIT of Silicon Valley," Goldstein says.