The old adage has it that audio is 90% of video. It's likely true. An audience will probably forgive weak video, but won't put up with bad audio.
Do a search at B&H or Adorama for a shock mount & shoe clips. Rode SM3 is one I recommend, Pearstone DUSM-1 is a clone of it, and you'll you others, too.
You'll want a highly directional shotgun microphone. I have two Audio Technicas, (an AT879 - which I got with the Rode SM1 and a Low to High Impedance Matching Transformer (1.5') cable ---- that kit now has the Pearstone DUSM-1 shock mount, but still it's $249 for the kit and it's a good deal - search B&H # AUAT897K2 or you can see other Audio Technica kits by searching "Audio Technica Kits". My long shotgun is an AT815 and has a more narrow pickup.
As Tom said, getting good audio is hard, and if you are doing this professionally, you'll do yourself proud to have someone who knows what their doing do it for you. That'll take a load off you.
That said, if I have to do it, I try to make sure that my audio is taken from a microphone off camera if the subject is static (such as in interview), and is speaking into the mic as much as possible. Ideally, I'll capture two versions of the session, one short gun on the mic stand into a digital recorder (TASCAM DR100) and another track on the long shotgun (which is likely also on a stand) into the D7000 (I'm waiting for my D800 ;-0 ). That last track is terribly important; it's the synchronizing track to the first track, or if both are great, and sometimes, I'm lucky, it becomes the stereo track when that is available. Depending upon which software one uses, the waveform of the audio makes the synchronization easy.
I would have some additional recorder. I have two TASCAM devices, but there are others. You might want to consider that audio microphones are typically XLR or 1/4" inputs and the inputs on DSLRs are not (3.5mm), so that's a pain. A Low to High Impedance Matching Transformer cable will be necessary for connecting to the camera and possibly to the device, if you decide to get one.
You haven't asked about wireless microphones, but I also have two of those. They are old and tired like me. I use them only when I have to, and they provide some good results. The best are god awful expensive and sound terrific, but sterile and vacant. Don't expect to get anything under $600 a kit to produce much that will sound any more than amateurish. If you have the opportunity to listen to Late Night with David Letterman or the Tonight Show with Jay Leno, compare that with much superior (content wise) Charlie Rose (sorry everyone not in the USA - I've forgotten a lot other programming), Rose's programming is so clear you can hear each phoneme as it is pronounced, but Letterman and Leno is more like human sound, a tad musty and noisy. Rose's show is almost like an operating room it is so clean.
You pay a fortune to get the sound like Leno and Letterman, it's a magnitude beyond Rose's show in the nature of sound quality in that has been made more 'natural' by be less quality... Funny, huh?
Their microphones, of course, run into 4-5 figures before the transmitters and receivers are even considered.
I've shot for several shows and networks, but I'm mostly retired, now. The last thing was a few scenes for PBS that I doubt are going to make it into the final show. The subject was elderly and the interview didn't go so well. There might be a few cutaways, but we'll see.