If you like Gregor the Overlander by Suzanne Collins

If you liked the Gregor books, you might
like one of these:

City of Ember by Jeanne Duprau (and sequels).

In the year 241, twelve-year-old Lina trades jobs on Assignment Day to
be a Messenger to run to new places in her decaying but beloved city,
perhaps even to glimpse Unknown Regions.

Island of the Aunts by Eva Ibbotson.

As they get older, several sisters decide that they must kidnap children
and bring them to their secluded island home to help with the work of
caring for an assortment of unusual sea creatures.

Amulet of Samarkand by Jonathan Stroud.

Nathaniel, a magician's apprentice, summons up the djinni Bartimaeus and
instructs him to steal the Amulet of Samarkand from the powerful
magician Simon Lovelace.

Magyk by Annie Sage.

After learning that she is the Princess, Jenna is whisked from her home
and carried toward safety by the Extraordinary Wizard, those she always
believed were her father and brother, and a young guard known only as
Boy 412--pursued by agents of those who killed her mother ten years
earlier.

Artemis Fowl by Eoin Colfer.

When a twelve-year-old evil genius tries to restore his family fortune
by capturing a fairy and demanding a ransom in gold, the fairies fight
back with magic, technology, and a particularly nasty troll.

Suzanne Collins has another book coming out this fall that sounds great.
It's the first in a new series and it is called The Hunger Games.
Something for us to look forward to!