What makes a good chalkboard?
The good chalkboards appear to be made of porcelain enamel fused to a steel core. See this site for more details on the manufacturing process. As JeffE mentioned in a comment on another answer, cheaper chalkboards are made by painting wood or chipboard with a special chalkboard paint. Although these are good for crafts, they are NOT the kind you want to have in a classroom. They have to be primed with chalk before the first use and after being cleaned with a damp cloth. Also they will often have to be given another coat of paint after being used for a while.

For non-squeak writing, break long pieces of chalk in half--this will usually take care of the problem! I have noticed that regular, i.e. daily, sponging with an all-purpose cleaning solution also helps to prevent smearing while writing/erasing.