This is a Balmoral bonnet.

The "pom-pom" on the top is called a toorie. It's pretty much standard on Balmorals. So is the ribbon in the back, which people either wear loose or tied in a neat bow (my preference). You can order one with or without a diced band. Black is a fairly standard color, but others are available. The patch of ribbon on the side is where you would affix your clan badge.

By comparison, this is a Glengarry.

Different style, but you have the same features/options as you do with the Balmoral, only the ribbons in the back are always worn loose with this cap, never tied.

The style of cap Mael Coluim was recommending is our hand knit bonnet.

This is an older style, and a forerunner of the modern Balmoral. These are knit to order, and do not include the ribbon patch for a clan badge, nor the grosgrain ribbon in the back. They can be ordered with or without the toorie on top, and also come in a variety of colors.