It isn't on the official NBC website, but according to the AGTNews website, the first 12 quarterfinalists are...
ANNA GRACEMAN (Singer)
DEZMOND MEEKS (Singer/Pianist)
DUO AERO (Trapeze Artists)
ECHO THE PARROT (Animal Act)
FEARLESS FLORES FAMILY (Daredevils)
J. CHRIS NEWBERG (Comic/Musician)
MIAMI ALL-STARS (Dance Crew)
SANDAU TRIO RUSSIAN BAR (Acrobats)
SNAP BOOGIE (Dancer)
SQUONK OPERA (Band)
THE FIDDLEHEADS (Bluegrass Band)
THOSE FUNNY LITTLE PEOPLE (Variety Act) (They are the gnomes Piers seems to hate)
I remember ten of them by name (the two I don't are The Fiddleheads and Duo Aero).
This list might be inaccurate, but we won't find out for sure until Tuesday (I think).