The Chef's Knife
The chef's knife is your primary tool in the kitchen, it's used for practically all your slicing, dicing, chopping and mincing. A quality chef's knife will make your life easier and taking proper care of it is essential.
The standard chef's knife is approximately 8 in. in length although you can get them anywhere from 6 in. to 14 in. There are two main styles of chef's knives; the German style with a more rounded blade providing you the ability to rock the knife back and forth for chopping, and the French style with a more triangular blade, more well-suited for slicing than chopping.
The German style chef's knife is definitely the more common but it's a completely personal preference as to which you should use.
There is also the santoku knife, a knife similar to the chef's knife and used in many of the same actions. Read about the santoku knife here.