How do you get onto the list? Well, that's simple!
If you are ready for a Battleground or two within the next hour, head over to the start page and choose your faction. That will take you to a page with an IRC window and an entry screen below it. Type in your realm and your character's name in the entry screen to retrieve your basic details from the Armory. You can add in notes and doublecheck that your main spec and off spec are correct.
Note the IRC Name section -- this is where you fill in the name that you're using in the live IRC chat above. This way, you can give yourself an IRC name of your choosing and seek out Rated Battleground buddies with any character. Other IRC users will see your name in the list and can contact you directly -- and you're off! Your entry stays up for an hour, so if you're looking for groups further in advance, you can head over to the Battlemasters Forums and make a post.
As an aside, the Horde chat seems currently rather more popular than the Alliance chat, hence the split channels. As a mainly Alliance player myself, I'm not OK with this! So I'm putting the call out to my fellow humans, dwarves, draenei, worgen, gnomes and night elves: People of the Alliance! Get on over to The LFG List and get involved!