I love collards, mustard greens, kale, the whole shebang... including and maybe even especially in raw juices.  I have three charts in my blog listing the foods with calcium to prove there are more plant sources with higher calcium than milk, including human milk which is listed last.  You can check them out here...  

http://curezone.com/blogs/m.asp?f=573&i=15
http://curezone.com/blogs/m.asp?f=573&i=16
http://curezone.com/blogs/m.asp?f=573&i=17

I think it's quite apt that collards et al., are considered SOUL food.  They're so delicious with powerful healing properties that they not only heal the body, they touch the spirit.  I think of this family as the happy veggies.  I honestly believe that it was the collards and kale I profusedly drank that made my recent 30 day juice fast go so smoothly.

Great blogs, Ren!  I've really been enjoying your writing and style of thinking!

All the best!

~ Dazzle