An example of what was very probably the earliest Indian coin: a large silver shatamana (double siglos or bent bar) issue, Gandhara, c.600-500 BCE (43mm long, 10mm wide)

Source: ebay, May 2007

A closer view

Source: http://www.vcoins.com/ancient/pegasi/store/viewitem.asp?idProduct=4738
(downloaded Nov. 2007)

Another example of this kind of coin

Source: http://www.grifterrec.com/coins/india/ancientindia.html
(downloaded May 2007)

These coins came in a shorter, wider shape also

Source: http://www.vcoins.com/ancient/ecin/store/viewitem.asp?idProduct=6038
(downloaded Nov. 2007)

"Taxila, Short Silver Satamana Bent Silver Bar, c. 600-303 BC. One of the earliest coins in the world, these silver bent bars were mentioned when the King of Taxila paid off Alexander the Great. This type is somewhat scarce. Size: 25 mm."

And one more example, showing the curvature these coins often had

Source: http://www.med.unc.edu/~nupam/ancient1.html
(downloaded May 2007)

*Punchmarked coinage of the early Kingdoms, Gandhara - Mauryans (6th c.BC - 3rd c.AD)**, a research page from Ancient Coins Canada

A punchmarked bar coin of the "short debased" type from the mint at Taxila, c.450 BCE

Source: http://www.vcoins.com/ancient/ecin/store/viewItem.asp?idProduct=2315&large=1
(downloaded Oct. 2006)

"Taxila Bent Punchmarked Bar c. 450 BC. Billon Debased Early Type. Crude fine, with some adhesion. Size: 24 mm.Weight: 11.20 grams."

A Persian siglos coin from the time of Darius I, and bearing his portrait; Gandharan coins were calibrated to the siglos (see the research site above)

Source: http://www.vcoins.com/ancient/frankkovacs/store/viewItem.asp?idProduct=1088&large=1
(downloaded Sept. 2006)

"Persian Kingdom. Darius I, 521-486 BC. AR. siglos of Sardis (5.20 g). Half-length figure of the Great King r. / incuse punch."

Another early Persian siglos coin probably from his reign, c.505-480

Source: http://www.vcoins.com/ancient/bpmurphy/store/viewItem.asp?idProduct=4747&large=1
(downloaded Sept. 2006)

"Achaemenid Empire. Circa 505-480 BC. AR Siglos - 14mm (5.34 g). Persian king or hero in kneeling/running stance right, drawing bow / Incuse punch."

A siglos perhaps from the reign of Artaxerxes I (c.485-470 BCE)

Source: http://www.vcoins.com/ancient/civitas/store/viewItem.asp?idProduct=8525&large=1
(downloaded Sept. 2006)

"Persia Achaeminid Kings Traditionally attributed to Artaxerxes I Circa 485-470 BC. AR Siglos 5.63g. 17mm. Persian warrior-king kneeling or running right, holding bow before, spear at side; small crescent-shaped banker's mark on obverse. Plain incuse punch."

A silver 1/8 karshapana coin from the mint at Taxila, c.400's BCE

Source: ebay, May 2007

A slightly later silver karshapana, c.370-320 BCE, from Taxila

Source: http://www.vcoins.com/ancient/ancientimports/store/viewitem.asp?idProduct=13277
(downloaded May 2007)

"Ancient India Taxila-Gandhara Mauryan denomination Silver Karshapana punchmark coin, 370-320 BC. Obverse: Many interesting punchmarks, including dog and rabbit. Reverse: Single punchmark shaped like a 3. Size: 19.36 mm. Weight: 2.6 grams."