Kendamaspot - Recently re-launched. Includes a great set-up tips page.
El Balero - History page with lots of info on the kendama's forerunner, the bilboquet.
Takarabako newsletter - Taken from Takarabako, a resource for teachers engaged in Japanese language education, this PDF newsletter (<--Right-click to download, 1MB) has an interesting article about a cultural exchange trip to Mongolia, featuring kendama, of course!