Ok, I'll admit, I've not read EVERYTHING she's written. I'm only halfway through the protector of the small series and haven't yet picked up the Becca Cooper books or Melting Stones. However, I've read the rest and am working my way through rereading them and they certainly stand up to their memory, which not many books do.
There are two places to start with Tamora Pierce books. The first is Tortall - home of Alanna. The main story here is a girl who wishes to be a knight in a world that doesn't allow it. She switches places with her brother and hides her identity to reach her goal. Other series in Tortall are those of Daine, a wild mage who speaks with animals, Kel, a girl who wants to follow in the footsteps of Alanna after it's decreed that girls can now become knights, and Alanna's daughter, who is a very different sort of person.
The second world is Emelan - a world filled with an abundance of mages. The stories of this world follow four young mages with very different powers and backgrounds. These are more stories of building friendship rather than ones of personal growth and triumph, though the second series sees the friends going on their own journeys.
There are too many books to go into detail for all of them - and I'm afraid I can't really pick a favorite to write a proper review. But these are certainly books to look into if you've never seen them. They are, mostly, fairly short books which makes one of the quartets the perfect thing to fill a free weekend.