In the United States... sometimes...

The $100 bill can be called a "Benjamin."

There are more $100 bills circulating in countries outside the United States than there are within the United States.

I don't know any nickname for the $50 bill or the $20 bill.

The $10 bill can be called a "sawbucks."

The $5 bill can be called "fin" or a "fiver."

The $2 bill is hardly ever seen, it's all very weird... supposedly, some people think $2 bills are bad luck, and that's been enough to all but drive them out of circulation. Nowadays if you do have a $2 bill and hand one to a cashier, they may look at it for a long time and call a manager to be sure it's real, because they've never seen one.

The $1 bill can be called a "single."

The paper bills are made out of special paper manufactured in only one factory, the Crane Paper factory in Dalton, Massachusetts. I've been in Dalton but didn't have time to visit the factory. The US Senators from Massachusetts work hard to convince the government to use only that company as their supplier.

All US paper bills are exactly the same size and color. Cashiers are trained to look hard at them, actually read the numbers, and be familiar with the different portraits on them

There are a number of $1 coins and the government keeps trying to put them into circulation but the public doesn't like them, and, again, you hardly ever see them and there's no name for them.

The $0.25 coin is a "quarter" or, not all that common but you do hear it, "two bits." 

The $0.10 coin is a "dime."

The $0.05 coin is called a "nickel," but I don't think they've actually made them out of nickel in my lifetime.

The $0.01 is a "penny." They are a real nuisance. Due to inflation they are next to useless, and they actually cost the government 1.7 cents to make one. They persist, possibly due to the influence of the zinc lobby.

Hi! I am from Turkey. We use Turkish Lira Code: TRY (usually abbreviated as TL) Sign:  ₺

Bank Notes:Each bank note has Atatürk's portrait on the obverse(front). On the reverse(back), one of the famous people in Turkish history is featured.

200 TL(purple): This one has a portrait of Yunus Emre (a folk poet from 13th century) on the reverse.

100 TL (dark blue): This one has a portrait of Itri (a Turkish musician from 17th century) on the reverse.

50 TL (orange): This banknote has the portrait of Fatma Aliye (novelist and women's rights activist of the 19th century).

20 TL (green): This one has the portrait of Ahmet Kemalettin (an architect from the 19th century).

10 TL (pink): This banknote has a portrait of Cahit Arf (a mathematician from the 20th century).

5 TL (brown): This one has a portrait of Aydın Sayılı (a historian of science)

The currency subunit is kuruş.We have the coins of 1 Turkish Lira and 50,25,10,5,1 kuruş.(1 kuruş is not used generally). Each coin has Atatürk's portrait(front) and traditional patterns(back).

I'm in the United States. I think the whole world knows our currency =)

(Yes, it's the ugly green one. We stubbornly refuse to make it multi-colored because we're just that stubborn =P )

Interesting topic, @Lawrence! Nice to know about the currencies of other countries.

Well, recently India went through a huge currency exchange phase. It is termed as demonetisation. So the Government of India demonetised the higher denomination currency note like 500 rupees and 1000 rupees. It was a surprise announcement by the PM of India to revoke these two notes. Everybody got shocked but all supported this move. So all went to the bank to exchange it with the new 500 rupees note and newly introduced 2000 rupees note. The design of these two note is nicer than the other notes.

People use 1 rupee, 2 rupees, 5 rupees and 10 rupees coins as well as paper notes. There used to be some coin like 5 paise, 10 paise, 20 paise, 25 paise and 50 paise coins, but nowadays, those are not acceptable in the market and also the RBI(Reserve bank of India) has stopped making them. ** 1 rupee=100 paise

Now coming to the paper note bill, so there are 20 rupees, 50 rupees, 100 rupees, 500 rupees, 1000 rupees(but currently unavailable due to demonetization) and 2000 rupees(newly introduced). But the RBI has the power to print any value of bill up to 10,000 rupees. Sometimes RBI releases some coins of high-valued bills in the commemoration of some great people on the eve of their birth anniversary.

I live in China, but I'm from Canada. In Canada we have these notes: 100$ (brown), 50$ (red), 20$ (green), 10$ (purple), 5$ (blue), and we have these coins: 2$, 1$, 0,25$, 0,10$, 0,05$. Our bills are in a special material called polymer. It looks and feels like plastic.

The bills: https://en.wikipedia.org/wiki/Banknotes_of_the_Canadian_dollar ;
The coins: https://en.wikipedia.org/wiki/Coins_of_the_Canadian_dollar#Specifications