Check out the Horde Guild Directory for a list of guilds on the server.
Firebrand Enterprises is always hiring too, but we don’t really do a whole lot of dungeon content. Basically we do the occasional transmog/achievement run and some mythic content a couple of hours once a week. Sometimes a couple of Timewalking dungeons when they’re up. I can’t honestly recommend us for someone seriously looking to progress in endgame content unless you don’t mind using us as a stepping stone.