I'm using
this Coodio cover from my Glo on the Glo HD and it fits perfectly. It's a bit sturdier than the other generic magnetic covers, the front flap particularly seems more solid and not near as flexible, and this particular cover never had the problem of shutting off the reader because of a too-strong magnet when the flap is folded over while reading. They had more colors at the time I ordered though, I have a medium shade of blue which I like.
I also have
the more generic sleep covers which also fit perfectly, but the front flap seems a bit more flexible than the Coodio. Otherwise they also work and fit just fine.