I'm partial to dark chocolate, personally. A nice, smooth dark chocolate with a chocolate ganache filling is usually great with whatever black or dark oolong you choose to serve. I think that semisweet chocolate (like semisweet chocolate mousse) would go well with a good pu-erh.
If you're serving a lighter oolong, a green. or a white, I'd recommend something chocolate-flavored (instead of actual chocolate) because any kind of chocolate is going to overwhelm the taste of the tea. Maybe wafer crisps with white chocolate filling? Another idea is to make a white-chocolate whipped cream and serve it on the side with fresh fruit.
I don't generally drink herbals or rooibos, so I can't suggest anything for those.
I'd love to know where you found an earl grey-flavored chocolate - I'd love to try that!