Speech Level Singing (SLS) is a singing technique that aims to make singing as easy and natural as speaking.
Seth Riggs, creator of the technique, has a good Q & A style summary here.
Brett Manning also teaches Speech Level Singing in Nashville, his site Brett Manning's Singing Success. Here are also The 9 Biggest Lies About Singing according to Brett Manning.
I've been singing for a long time, but only very recently discovered SLS. I'm currently taking lessons from Emil Svensson, a great teacher that I can warmly recommend to anyone who wants to improve their singing.
You can read about my experiences below:
Also, up to the minute notes can be found here.