[From the archives. This miso primer was published here last September (2008). I've added some notes about miso-based blends, especially sumiso or miso with vinegar.]
This is a post that has been a long time coming. I kept on holding it off until I had a good variety of miso on hand to show photos of. I can't say I have a comprehensive selection to show you, but I hope you will find this article useful anyway.
Miso （味噌、みそ), as you probably know already, is a naturally fermented paste made by combining cooked soy beans, salt, and often some other ingredient such as white or brown rice, barley, and so on. The texture can range from smooth to chunky, and the color from a light yellow-brown to reddish brown to dark chocolate brown, and the flavor ranges from mildly salty and sweet to strong and very salty. It is packed with umami and protein, not to mention all sorts of nutrients.
Miso-like fermented bean products and pastes exist all over Asia, but here I will mainly limit myself to the most commonly used Japanese misos.