In principle there are four types of ramen;

1. Shio is “salt” and this ramen is probably the oldest of the four. It is a clear, yellowish broth made with plenty of salt and any combination of chicken, vegetables, and seaweed.  Noodle texture and thickness varies among shio ramen, but they are usually straight rather than the curly types.

2. Tonkotsu is “pork bone”; not to be confused with tonkatsu. This ramen usually has a cloudy white colored broth. It has a thick broth made from boiling pork bones, fat, over high heat for many hours, which suffuses the broth with a hearty pork flavor and a creamy consistency that rivals milky butter.

Most shops, but not all, blend this pork broth with a small amount of chicken and vegetable stock and/or soy sauce. The noodles are thin and straight, and it is often served with beni shoga, a pickled ginger. In recent years the latest trend in tonkotsu toppings is māyu, a sesame oil, a blackish, aromatic oil made from either charred crushed garlic or sesame seeds. It is a specialty of Kyushu, particularly Hakata-ku, in Fukuoka, hence sometimes called “Hakata ramen”.

3. Shōyu is “soy sauce” or as I say shoyu in Japanese. This is ramen typically has a clear brown broth, based on a chicken and vegetable (or sometimes fish or beef) stock with plenty of soy sauce added resulting in a soup that is tangy, salty, and savory yet still fairly light on the palate.

Shōyu ramen usually has curly noodles rather than straight ones, but this is not always the case. It is often adorned with marinated bamboo shoots or lactate fermented menma, green onions, kamaboko, fish cakes, nori, boiled eggs, bean sprouts and/or black pepper; occasionally the soup will also contain chili oil or Chinese spices, and some shops serve sliced beef instead of the usual chāshū. http://en.wikipedia.org/wiki/Char_siu

4. Miso ramen is a newcomer, having reached national prominence around 1965. This uniquely Japanese ramen, which was developed in Hokkaido, features a broth that combines copious amounts of miso and is blended with oily chicken or fish broth, and sometimes with tonkotsu or lard – to create a thick, nutty, slightly sweet and very hearty soup. Miso ramen broth tends to have a robust, tangy flavor, so it stands up to a variety of flavorful toppings: spicy bean paste or tōbanjan; http://en.wikipedia.org/wiki/Doubanjiang They can also add, leeks, onions, bean sprouts, ground pork, cabbage, sesame seeds, white pepper, and chopped garlic are common. The noodles are typically thick, curly, and slightly chewy.