I amused myself in Cambodia by spending $2 bills. People took them but they were a great novelty. frotz and jayhawk should come to Cambodia and dole them out. :)
The poorer the country, though, the crappier their paper money tends to be. Hardly a surprise; if your country can't even pay its bills it's not like they can afford to print more. As a result some amazingly stained, torn, taped-together bits of barely-recognizable paper get passed around as money. In some countries people refuse notes with rips, but this hasn't been a problem for me so far.
Zimbabwe was the first place I'd been to where the inflation was so bad that the country hadn't kept up by issuing notes with progressively larger denominations. In Zimbabwe, the Z$1000 note had just come out when I'd arrived, and it was fairly hard to get one. When I changed US$40 I got a huge brick of Z$500 notes, at about Z$3600 to US$1.
I've also found a lot of cheap copies of crown-sized silver coins in the markets in Laos, Cambodia, and Thailand. Originally I saw a lot of really bad cast copies, but in Chiang Mai, Thailand, I started to see obvious restrikes. I've seen copies of Maria Theresa thalers, British trade dollars, Morgan dollars, Chinese yuan, and Japanese yen. All of them are obvious fakes. The two funniest of these were in the gift shop at the Silver Temple in Phnom Penh. One was a Ugandan 5 shilling piece from sometime in the '80s, and the other was a St. Helena and Ascension Charles and Diana royal wedding 50p piece. I don't even think the originals from which they were copied were actually made of silver. The castings had had their 1980s dates crudely changed to 1900s dates.