Transparent water color: Paints as a dye and soaks into the surface of the paper. Transparent uses lots of water and colors and are designed to move through each other giving interesting effects. Transparent can be thinned out and used as a glaze on top of other colors. It is most popular because of the softness it can create when wet paint is applied over a wet surface.
Gouache: A little more fluid but best for large areas where the colors need to dry to an evenly velvet finish. Large brilliant colored areas without streaks. Covers well over darker surface and holds color well. Very light fast for permanency.
The most valued difference is it comes back to life if when re-wet.
Tempera: A less expensive gouache used mainly on schools and posters. Kids like it because it's easy to use and washable.
Egg Tempera: An older technique used by mixing egg yolk into the paint (usually gouache) for permanency. The technique is used by artists like Andrew Wyeth, and is becoming popular today because of the polychromatic effects, that it gives the painting. Wyeth painted up to 12 different colored washes over a white wall. The egg makes the paint permanent when it dries.
Fresco: Painting over the top of wet plaster. When it dries the colors are embedded in the plaster and is very permanent.The last supper by Leonardo de Vinci is a fresco. The Sistine Chapel that was painted by Michelangelo is a fresco. Very popular in early times on large wall murals.
Acrylics: Some say this is the best of all worlds. They are close to oils as any othe medium. Vivid in color, they cover well and the can be used like a transparent watercolor. They work well on board or paper. They are very permanent like oils. Those who use acrylics swear by them.
Do some of your own research, and try some or mix them up with each other.
More to come...