What is as good drawing program to use for simple drawing/sketching?

Paintool Sai Is a very simple program with some really good features.. I use it for almost everything now.. The pen tool in Sai is amazing and unlike photoshop very easy to work with.. You may still want to use photoshop for coloring but for sketching and simple drawings you use this program It even opens and lets you save in PSD format for ease of use with photoshop..