iPhone / Video Camera Audio Options - All Price Ranges
[Note: keep the mic close to the mouth (12" or less) - do not use shotgun or camera mounted mics]

BEST OPTION FOR GREAT AUDIO (lavalier) into your iPhone: Use
CablesOnline 6in 3.5mm StereoTRRS 4-Pole Male to TS Microphone iPhone Adapter, Black (IP-MIC2K) to hook up a Giant Squid lavalier mic to an iPhone. Special Note: I've found that it's best to lock the iPhone down on a tripod and then plug in the mic adaptor and then launch the camera app. See my review of the Giant Squid Mic (an affordable made-in-the-USA lavalier mic that sounds great): http://youtu.be/-naG9v-xhGo You can also use the Giant Squid mic with a ZOOM H1 recorder.

Note: Keep in mind the Giant Squid mic can also be plugged directly into most cameras with mic input jacks without an adaptor. You will want to keep an extension cable in your kit incase the Squid's 5 foot cable is too short. 

My google+ friend Bruce Turner recommended a Comprehensive iPhone Mic Adapter cable for hooking up an XLR mic to the iPhone. IMO this is a great plug-and-play solution for getting great audio into the iPhone. Especially for interviews in the field. Put your iphone on a tri-pod using The Gliff (another must-have iPhone 4 or 5 accessory - now also available for the 6 and 6 plus) and then plug in this cable. Plug in a Shure SM58 and you're good to go. You do need to speak right into the mic but this is a good thing as this will help keep background noise down.

I bought the cable on Amazon for $29.95 and got FREE shipping with Amazon Prime. I'm ordering another one today to have as a backup and to keep in my second kit. Amazon link: http://www.amazon.com/Compatible-Microphones-Professional-Recording-Headphones/dp/B004Z97CQW

The Comprehensive iPhone Mic Adapter cable setup is for iPhone or andriod phones. Special note: To hook a mono mic like an SM57 or 58 to a stereo camera like
the Sony NEX-7 you can use this simple cable: http://www.amazon.com/HOSA-XLR-3-5mm-Sleeve-wired/dp/B000068NZC/ To mount your smart phone (iPhone or andriod) on a tripod use this: http://www.amazon.com/gp/product/B005LY9FVU/ Note: Lock down the phone first and then open the camera app.

Sennheiser EW100 wireless kit I use: http://www.amazon.com/Sennheiser-EW100ENGG3A-100-Diversity-Frequency/dp/B002CWY0C8/ - my video: https://www.youtube.com/watch?v=JZzBAJ9ND0A Also see: https://www.youtube.com/watch?v=yJ06qn0czak and for iPhone 5 & 5s users see: http://www.amazon.com/Glif-Plus-deluxe-package-iPhone/dp/B00AAKO646/

More product links on amazon:
Rode Smartlav Lavalier Microphone for iPhone and Smartphones:
http://www.amazon.com/gp/product/B00BHN05H2/
extension cable for Rode Smartlav:
http://www.amazon.com/gp/product/B008DWGLLO/ (make sure cable is plugged in all the way when using)
http://www.amazon.com/gp/product/B00E3ZJQ62/ (use this shorter cable if using the Apple leather case)
http://www.amazon.com/CablesOnline-StereoTRRS-Microphone-Adapter-IP-MIC2K/dp/B00EG0OBYQ/ (use this cable to hook up a Giant Squid lavalier mic to an iPhone)
Want a way to clip your iPhone or a ZOOM H1 recorder to your talent? Use this:
http://www.amazon.com/gp/product/B000PIHG9U/ (Universal Cell Phone Flip Case)

Glif Plus: A deluxe Glif package, iPhone 5 Tripod Mount & Stand:
http://www.amazon.com/gp/product/B00AAKO646/

F-S(Y): i.Trek SUPER MOUNT F, Metal Smartphone Tripod Adapter:
http://www.amazon.com/F-S-Smartphone-Motorola-Blackberry-Smartphones/dp/B005LY9FVU/
Special Note: Be sure to lock down the iPhone on the tripod prior to turning on the camera app.

This video is also worth watching: http://www.youtube.com/watch?v=U2fYf970GAM
Finally here's a test of the Rode SmartLav using the iOS app: https://soundcloud.com/craigshipp/recording-5

Looking for the cheapest and easiest way to get good audio into your phone? Check this out:
extension cable link: http://www.amazon.com/gp/product/B008DWGLLO/
(make sure cable is plugged in all the way when using)
this shorter cable has a thinner plug so it's a great option if you use the Apple leather case:
The great sounding Giant Squid Mic can also be plugged into an iPhone using:
http://www.amazon.com/CablesOnline-StereoTRRS-Microphone-Adapter-IP-MIC2K/dp/B00EG0OBYQ/ - 
You can also use the Giant Squid mic with a ZOOM H1 recorder and then sync the audio in post.

The Giant Squid can also be plugged into your mic input on most cameras including Sony.
It comes with a five foot cable so also get an extension to keep in your kit.

For hooking up an XLR mic to my Sony NEX-7 or NEX-VG10 or other video cameras:
HOSA XLR (F) - 3.5mm Tip/Ring/Sleeve, (wired for dual mono), 1 ft.
http://www.amazon.com/HOSA-XLR-3-5mm-Sleeve-wired/dp/B000068NZC/

If you own a Sony camera with the multi-interface hotshoe here's a wireless system that's very compact:

Sony ECM W1M Bluetooth Wireless Microphone System

Sony ECM W1M Bluetooth Wireless Microphone System