First, a rule of thumb: Use a serif type for the body and a sans serif type for the headlines. Many people who make their living in publishing think this "rule" is true. But like many rules that involve taste, many don't agree at all.
A typical body type is Times or Times Roman. You'll find that many newspapers and magazines use this type for a body type. It continues to be the most common type and, because of this, we are at least used to seeing it.
A typical sans serif headline type is Arial, but this type is considered very uncool. You can get a headline type that is just as clean and attractive as Arial, but not uncool, if you choose Helvetica or even Futura. You might well have to buy these typefaces (fonts) from a major online type provider. Check out the ads below. Most online vendors offer suggestions as to appropriate typefaces and will let you download the fonts.
Another way to choose a typeface for your newsletter is to look around. Look at printed things: brochures, magazines, newspapers, other newsletters and find a style and "look" you like. When you see a type you like, you can use any of several magical online type finders that will allow you to identify it. This is actually a very interesting way to get to know a typeface. Try it! Below you will find some letters from a certain font. Use the creative pro type finder to identify it.