What we R&B in the 21st Century really is exactly the same Hip-Hop - the only difference is that in what is considered R&B, the vocals are sung and not rapped. Many artists deemed to be R&B are also considered Hip-Hop. The same producers who produce Hip-Hop produce R&B. So to be safe I suppose we should just call things R&B/Hip-Hop.
Prominent R&B artists include: Usher, Beyoncé, Ne-Yo, Mary J. Blige, etc.
Prominent producers include: The Neptunes, Timbabland, Kanye West, etc.