This new version of my encoding detector has many improvements over the previous version, including the ability to run as a stand-alone program. It can detect most major Chinese, Japanese, and Korean encodings, and can tell whether a file uses GB-2312, GBK, GB18030, HZ, Big5, EUC-TW (CNS), ISO-2022-CN, EUC-KR, Windows Korean (CP949), ISO-2022-KR, Shift-JIS, EUC-JP, ISO-2022-JP, ASCII, UTF-8, Unicode or OTHER if none of the above.
You can also type web addresses into the "Source File Name" field to see what encoding they use (must use "http://" with the web address).
Set-up Instructions are available at the Java Set-up page.