I have about a dozen different ones. Some are made to look like US currency. Unfortunately, some dealers put these with the "100 notes for $30" packages, as if they are real. I buy them now at Chinese and Vietnamese grocery stores, usually around $2 for a pack of 100. They are called "joss paper," and are among the types of papers burned to honor the dead. They can usually be found near incense in the stores.

Here is a link to a currency page with some of them:
http://www.zzzcoins.com/currency.htm