The Augustus of Prima Porta (photos 1 & 2), now in the Vatican Braccio Nuovo, appears to be based on the Doryphorus of Polykleitos, which portrays what Polykleitos saw as the ideal proportions for an athlete. The Augustus statue shows him as a victorious general making a speech, posed in the traditional controposto manner.

It was discovered at Prima Porta, near Rome in 1863, in the villa belonging to Augustus's wife Livia. It is probably a copy of a bronze original from 20 B.C. The copy dates to the early reign of Tiberius (~15 A.D.) and includes, on its breastplate, scenes of the Roman victory over the Parthians, including a protagonist who may be Tiberius.
 

Augustus as Pontifex Maximus, from Via Labinaca (photos 3 - 6). This statue is usually dated to sometime after 12 BC, on the basis of the hair style (similar to that of the Prima Porta Augustus), other stylistic elements, and his finally accepting the office of chief priest upon the death of Lepidus around 13 BC. The head is carved from Greek marble and the body from Italian marble. Museo Nazionale Romano.

Octavian (later Augustus, photo 7) from the period 35 - 29 BC. Note the different hair style, identified by Vierneisel and Zanker as "Octavianstypus".

Musei Capitolini inv. MC413 (MC0413).

Portrait of Augustus in Greek insular marble (photo 8). Museo Capitolino Montemartini (Gasworks) inv. 2394. Found in excavations on Via del Mare near the Theater of Marcellus in 1937. The head is almost surely recarved from a portrait of Caligula. The forehead has been cut back to allow definition of Augustus's Prima Porta-style of coiffure. Rough, broad chisel marks are visible just below the hair line directly above the right pupil and at the hair line directly above the left exocanthion (point at the outer commissure of the eye fissure).

Portrait of Augustus thought to be reworked from a portrait of Caligula. Claw-chisel marks on the nape of the neck seem to betray removal of Caligula's "shag" style haircut. Our anthropometric analysis of the head opens some questions about this hypothesis.  J. Paul Getty Museum inv. 78.AA.261.
 

Portrait of Augustus for Caere (photos 15 & 16), recut from a portrait of Caligula. Note bulges over the eyebrows where the forehead has been cut back to accommodate conversion of Caligula's hair line to that of Augustus (Prima Porta configuration). Even in this small image, you can see the difference between the rough surface of the reworked forehead (just above glabella) and the smooth surface of the neck and cheek. Vatican Museum inv. 9953.

Sources:

Charles Brian Rose. Dynastic Commemoration and Imperial Portraiture in the Julio-Claudian Period (Cambridge Studies in Classical Art and Iconography), Cambridge University Press, 1997. ISBN-13: 978-0521453820.

Eric R Varner. Mutilation and Transformation: Damnatio Memoriae and Roman Imperial Portraiture, 2004. ISBN-13: 978-9004135772

Eric R Varner. From Caligula to Constantine: Tyranny & Transformation in Roman Portraiture, 2001. ISBN-13: 978-1928917014.

Klaus Vierneisel and Paul Zanker. Die Bildnisse des Augustus (Munich 1979).

Paul Zanker. The Power of Images in the Age of Augustus, 1990. ISBN-13: 978-0472081240.