Adding on to those sets in the Tortallan series are the two books of the "Daughter of the Lioness" (Trickster's Choice, Trickster's Queen) and the newest installment, "Beka Cooper" (Terrier). As of yet, Terrier is the only book in this series out.
Pierce also has books not set in Tortall out, like the "Circle of Magic" quartet (Sandry's Book, Tris's Book, Daja's Book, Briar's Book) and follows up on those with "The Circle Opens" (Magic Steps, Cold Fire, Street Magic, Shatterglass (I may have messed up the order there.)) Adding to that is "The Will of the Empress", which I'm not entirely sure belongs to a quartet, but follows "The Circle Opens".
Pierce edited an anthology called "Young Warriors".
In my opinion. Tamora Pierce is one of the most exceptional teen-fantasy novelists out there. Her work is filled with swords, sorcery, talking animals, animals that don't talk but probably should, humor, violence, and assholes you'd love to choke (and usually eventually die anyway, which makes it so much more satisfying).
Ms. Pierce got me into being an avid reader at a young age (and I'm only fifteen now). Therefore, if you want to get your child into reading, I suggest you get them a book by Tamora Pierce. Or read them yourself---they're all good. Her work is much better than that "Eragon" lord-of-the-rings-ripoff crap.
"By Tamora Pierce."
"OHMYGOD. Didn't I read a fanfic about Alanna killing Saphira before?"
"You did! I LOVED that. I wish it would happen."
"Yeah, Eragon sucks."
"I know. Pierce is so much better."
"Oh shiz, is that a randomly-placed H-bomb zooming at us?"