Here are several articles and presentations about TestNG (English, French, German).
TestNG has received a lot of help from various people throughout its existence.
With code:
Alexandru Popescu, who ported TestNG to JDK 1.4 and has been tirelessly contributing ever since.
Hani Suleiman and Mark Derricutt (IDEA plug-in).
Andrew Glover and Jesse Kuhnert/Brett Porter (Maven 1 and Maven 2 plug-ins respectively).
Jolly Chen (JUnitReport plug-in).
Thierry Janaudy (PDF report plug-in).
And also with ideas, articles and bug reports:
Filippo Diotalevi, Matthew Schmidt Robert McIntosh, JR Boyens, Robert Watkins, Aleksi Kallio, Doug Lea, Eron Wright, Guillaume Laforge, Owen Griffiths, Jean-Louis Berliet, Morten Christensen and many others...
A great product is nothing without testimonies, so here is what people have to say about TestNG:
"It's a lot of fun.  Not as fun as Seinfeld, but more fun than
Chris Rock on a bad day"
    - A buddy 
"Are you going to eat your dessert?"
    - Someone I met at the cafeteria
 
"Rock on, dude"
    - A skateboarder
 
"Okay, I'll try it.  Can I have my laptop back now"?
    - A scared contractor
 
"Cedric, stop talking to him, he's sleeping"
    - Some random person who should mind their own business