In order: Orthographic, Oblique and Isometric
Isometric drawings are 3D drawings drawn mostly on isometric dot paper. Oblique drawings are 2D images of 3D objects, and orthographic drawings are basically the same as an oblique drawing. The difference between oblique and orthographic drawings is that an orthographic drawing, when projected, 6 different pictures of the object can be seen, while an oblique drawing is just a 2D image of an object with forced depth.
Sited from: http://en.wikipedia.org/wiki/Oblique_projection