I'm honestly trying my damnedest to get #metal off the ground, but it's rather slow going. I wouldn't mind starting a Magic: the Gathering tag, but due to the colon in the name I have no idea how to go about it (since that would cause an issue with the current search functionality "tag:search goes here" Other than that, I guess the best piece of advice I can give is to check the Tags link at the top every so often; similarly to Reddit, new tags are being posted daily, so there should be a few that strike your fancy :)
I'll be adding to #metal soon enough. I've started posting music under #music and #music.CraigEllsworth, so when a metal track comes up I'll be switching from #music to #metal. I'm going to try to post a music track about once a day, and a fair number of my favorite bands are metal, so a pretty high percentage of what I post should fall under the #metal tag. Of course, people wishing to discuss tin and gold and stuff might steal the tag for their own nefarious purposes... :/
I'm a huge metal fan! I'll help you get it off the ground!