You can use this free downloadable dictionary program, CoJaK, created by Tal Liron, to look up words in Chinese, Japanese, and/or Korean. It's bidirectional -- you can look up the translation of an English word, or look up a word in Chinese, Japanese, or Korean to get the equivalent in English (or other Asian languages). It also includes standard romanization for each language. The definitions are taken from comprehensive scholarly online dictionaries -- CoJaK combines all their data in a handy program that lives on your computer and puts all the information side by side. This can be a very handy tool for anyone from beginners to professionals.
The program is Java-based, so it can run on any operating system that supports Java. However, right now the only simple installer available is for Windows (see installation instructions on the linked page for other operating systems). This is an open-source program under the GNU General Public License, so if you have programming experience you can also contribute to it!