We're looking forward to start using the Tascam DR70D. This sound recorder can record up to four channels as once. A really nice feature it also has, is the audio output. This allows you to connect the recorder right to the camera's mic port. Which essentially means the audio and video will be synchronized for us!
B&H Link: http://www.bhphotovideo.com/c/product/1086798-REG/tascam_dr_70d_4_channel_audio_recording.html