The next Nintendo Direct will be held this Saturday, April 21 at 12:00 p.m. Japan time (April 20, 11:00 p.m. EDT).
Hosted once again by Nintendo CEO Satoru Iwata, the presentation will cover 3DS and Wii updates.
You can watch it here when zero hour strikes.
Update: Nintendo of Europe will also host a Nintendo Direct. It will be held on April 21 at 1 p.m. CEST (7 a.m. EDT). View it here.