I buy it at a juice bar, fresh, (definitely the best), or buy the frozen packets at Whole Foods...

Here is my favorite brand of greens:
http://www.klamathbluegreen.com/klamath-blue-green-algae-products-main/klamath-blue-green-algae-products-main-page-blue-green-algae-superfood-afa-blue-green.html

Here is another one that I love. It is a mixture of amazing greens and enzymes. Add a scoop to your juice to make an amazing healthy drink:
http://www.amazon.com/Vibrant-Health-Green-Vibrance-Powder/dp/B004RBT964/ref=sr_1_7?ie=UTF8&qid=1323204324&sr=8-7

If you want wheat grass or barley grass, you can get all different brands on Amazon.com.

Where do you buy?

It is a superfood. Filled with nutrition. Yes, you should take it. You can buy it in powder/capsule form so that it doesn't taste so bad going down. Avoid any packed pills...they don't fully digest.

Other good "superfood" greens to consider are bluegreen algae, spirulina, and barley grass.

Do you drink it/eat it/take it? Should I?