The Samsung Galaxy S8 is expected to be powered by Qualcomm's Snapdragon 835 or the Exynos 9 chipset (depending on market) and arrive with a 5.8-inch 18.5:9 Super AMOLED touchscreen (and a 6.2-inch one on the S8+), 4GB of RAM, 64GB of base storage (expandable via microSD), a 12 MP f/1.7 main camera, an 8 MP f/1.7 selfie shooter, a USB Type-C port, and a 3,000 mAh battery (3,500 mAh for the S8+). It should run Android Nougat. The official announcement has been rumored to come on March 29, with availability in the US starting on April 21.
UPDATE: Here's another hands-on image of the Galaxy S8, showing its app list and on-screen buttons (a first for Samsung). As you can see, the order of the buttons is the same as for all of the company's devices sporting capacitive keys - with Back on the right.