There are many herbs and herbal extracts that have xanthine oxidase inhibition and thus may be useful in gout. Some of these include propolis and the flavonoid chrysin.

Xanthine Oxidase Research
Xanthine oxidase inhibitory activity and hypouricemia effect of propolis in rats.
Yakugaku Zasshi. 2005 Mar;125(3):315-21.Fancl Corporation Central Research Laboratory, Yokohama 244-0806, Japan.
The xanthine oxidase inhibitory activity of propolis from China and Brazil was measured. The propolis from both place were seen to have xanthine oxidase inhibitory activity. However, a stronger tendency was shown in the propolis from China. The compounds in each the propolis were measured quantitatively. A great deal of chrysin, galangin, and caffeic acid phenetyl ester were found in the propolis from China, an abundance of p-coumaric acid and artepillin C in the propolis from Brazil. Therefore it was revealed that the propolis compounds are very different depending on their place of origin. The xanthine oxidase inhibitory activity of these five compounds was measured. Caffeic acid phenetyl ester had the strongest activity, with chrysin and galangin next; p-coumaric acid and artepillin C showed weak xanthine oxidase inhibitory activity. We evaluated the hypouricemic effect of propolis from China on hyperuricemia induced by the uricase inhibitor, oxonic acid (500 mg/kg p.o., 1 h before the test drugs), and measured plasma uric acid values in rats. Oral propolis had a hypouricemic effect 2 h after its administration to oxonate-pretreated rats. These results suggested that a continuous intake of propolis may be effective for the prevention and the treatment of gout and hyperuricemia.