Separate mic for Nikon D3100?

I have a Nikon D3100 and want to record decent audio along with video, but the camera doesn't have a jack for a mic, any separate (good quality) recording devices anyone could recommed?

Well let me ask you a question. Have you ever done audio loop work? It's no picnic trying to match the audio to video but it can be done with the right editing program.

There's lots of audio records out there. Do some on line research and check the local shops.
I won't recommend anything specific, that's for you to decide.

I'm a fan of the Zoom H4n. Not knowing what your goals are, spending the money to upgrade to a D5100 might be a better long range plan, but if the want is to stick with the D3100 at least for now, the Zoom will do nicely.