Pronterface
Pronterface is a G-code sender and the graphical user interface of the host. It has a simple set of movement and temperature controls, as shown in the following screenshot:
By clicking on the model in the plate window, a pop-up window will appear. By holding Shift on the keyboard, the print layers can be examined by scrolling the mouse wheel. Refer to the following screenshot:
Printrun's easy interface and good operating features makes it a popular host for many RepRap machines. Its interface is not as sleek as some of the others, but it's a no-frills, dependable work horse.
A good tutorial on using Printrun can be found at http://www.plasticscribbler.com/tutorial/getting-started/item/21-getting-started-with-pronterface#.UxzyAPldUps.
A precompiled version can be downloaded from http://koti.kapsi.fi/~kliment/printrun/.