Bitcoin has always drawn comparisons to gold, and since the ‘early days’ (ca., 2011) gold and silver have been a popular thing to spend one's bitcoins on. Back then, we had hobbyist-like outlets such as Coinabul (if not 100% reliable), and today we have more than half-a-dozen serious coin- and bullion-vending brokers — all listed on Spendabit!
Bitcoin-accepting gold/silver dealers include JM Bullion, Veldt Gold, Oxbridge Coins, Bitgild, Amagi Metals, Zilvergoudwinkel, and All4btc. Plus, a number of merchants sell gold-plated “physical bitcoins”.
Additionally, we're happy to mention a new option for investing in gold via Bitcoin today. By searching for gold, precious metals, or similar items we'll now present you with a link to Vaultoro, a bitcoin-to-gold exchange. (Update: This has been disabled as of October 2019.)