GoFlight Technologies : a software update is available to syncrhonize your hardware with P3D v4.
FlyTampa : until they work on new updates, most of their sceneries are already compatible with P3D v4. The compatible sceneries are listed here, along the updates you need to download and install manually.
FSDreamTeam : In the same time they released KCLT Charlotte, their existing customers will also find a free update for KLAS Las Vegas (New Terminal 3 and control tower, SODE jetways), and P3D v4 updates for all their sceneries.
PMDG : Robert S. Randazzo communicated the detailed planning of updates release for all their current products line, from the latest 747-400 down to the DC-6 Cloudmaster. They expect to make them all during this month of June.
29Palms Scenery Design : the designers team announced they made updated installers for P3D v4 for the following airports : Magdeburg EDBC, Samos LGSM and Twentynine Palms KTNP.