Are you filming at the same time or just recording sound?
I use the RØDE Stereo VideoMic X with my camera which is a great mic for environment sound, but it works well for speech too if you're close.
I've used separate audio recorders before, but honestly, it's a pain to have to sync everything afterwards and find which clips match the audio. And you will find yourself not recording audio with every clip, etc. etc. It's not a very convenient workflow if you're also filming.