All you ever wanted to know (and probably a little more) about Japanese coins currently in use.
One Yen Coin
Here it is, the 1円. Incredibly light. Feels like a waste of time. Design is some kind of sapling.
Material: Pure Aluminum
Year of Issue: 1955
Five Yen Coin
Comes in two types, identical except for the fonts used. The old one (issued 1949) uses an old Chinese style typeface, while the one released 10 years later is more western. Coin is reminiscent of Ming-Dynasty Chinese coins but far less useful or valuable.
Material: Copper 60 - 70% / Zinc 40% - 30%, Weight: 3.75g,
Diameter: 22mm, Center hole diameter: 5mm,
Ten Yen Coin
Lovingly crafted bronze disc with a value of almost 7 pence! The design is "Houdo" temple in Kyoto. There are two types of 10yen, almost identical except one has a milled edge (issued 1951), and one has a smooth one (issued 1959)
Material: Copper 95% / Zinc 4 - 3% / Tin 1 - 2%,
Weight: 4.5g, Diameter: 23.5mm
Now we're getting into the big leagues! Hold on to your wallets! This cupronickel beast has a hole in!
Material: Copper 75% / Nickel 25%, Weight: 4g,
Diameter: 21mm, Center hole diameter: 4mm, Edge: Milled,
Year of First Issue : 1967
One Hundred Yen Coin
Can get you so many thing in the 100 yen shop (well, one. Plus tax). Made of the same stuff as 50yen coins and twice the price! No hole.
Material: Copper 75% / Nickel 25%, Weight: 4.8g,
Diameter: 22.6mm, Edge: Milled, Year of First Issue: 1967
Five Hundred Yen Coin Nickel-brass Coin
Material : Copper 72% / Zinc 20% / Nickel 8%, Weight : 7g,
Diameter : 26.5mm, Edge: Milled, Year of First Issue : 2000
An interesting (and yes, it is) thing about this coin is that it has NIPPON written in tiny letters, hidden around the "500" for piracy reasons (Arr). This Japanese site shows it in detail:
Images courtesy of this site.
Detailed information from here.