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); *another example, showing the bend*

Source: ebay, May 2007

Another example of these very early Gandharan silver bar coins

Source: http://www.vcoins.com/ancient/jencek/store/viewitem.asp?idProduct=5504
(downloaded July 2007)

"Gandhara, Circa 600-300 B.C. AR Shatamana (43 mm, 11.26 g). Gandhara symbol on each end."

One more of these very early Taxila "shatamana bent bar" coins, seen from all angles (length 11.3mm / 0.44 inches; weight 11.25 gm (100 ratti)

Source: ebay, July 2007

*An excellent research site on the earliest Indian coins** (Ancient Coins Canada)

A very early silver karshapana coin, with many punchmarks, from the Magadha janapada (c.500's-400's BCE)

Source: http://www.vcoins.com/ancient/coinindia/store/viewitem.asp?idProduct=99#null
(downloaded May 2007)

"MAGADHA: Series I AR punchmarked karshapana. Obverse  Five official punches, along with several banker's marks. Reverse  Banker's marks. Date  c. 6th-5th century BCE. Weight  3.34 gm. Dimensions  24 x 23 mm."

A punch-marked silver karshapana from the Kosala janapada, c.500 BCE

Source: ebay, June 2007

A silver 1/8 karshapana coin from Taxila, in the Gandhara janapada, 400's BCE

Source: ebay, May 2007

A silver karshapana from Magadha, c.300's BCE

Source: http://www.vcoins.com/ancient/coinindia/store/viewitem.asp?idProduct=113
(downloaded May 2007)

"Magadha: Series IVd Silver punchmarked karshapana, GH 425. Obverse  Five official punches. Reverse  One (or two?) unofficial banker's marks. Date  c. 4th century BCE. Weight  3.46 gm. Dimensions  20 x 13 mm."