you may also try http://cidian.youdao.com/ or http://g.iciba.com/ they r free too...when u install the1st one, u can save u some space n quite easy n the 2nd...more space..but with more function. I'm using the 1st...n quite ok

http://www.lingoes.cn/en/ it's completely free, you'll like it

Are you talking about for your browser or standalone software?

Firefox addon, only work within the Firefox browser. But it's good for learning, take a look: Perapera-kun: Chinese Popup Translator 2.1.1 https://addons.mozilla.org/en-US/firefox/addon/3349/

http://www.jukuu.com/；http://www.cibo.cn/；http://www.iciba.com/~try them~