New York-based Monster Worldwide, the online job posting site, said Friday that it has acquired Affinity Labs, a San Francisco-based operator of vertical Internet sites. Monster said it will pay $61M in cash for Affinity, which was venture backed by The Mayfield Fund and Trinity Ventures. Affinity raised a $10M funding round in December of 2006. According to Monster, Christopher Michel, Affinity's CEO, will join Monster as an executive. Michel was the founder of Military.com, which was also acquired by Monster in 2004. Goldman, Sachs & Co. advised Monster Worldwide in the transaction.