The user interface of LEO.org is much cleaner than dict.cc or equivalent.
Also you do not have to indicate the translation direction (as opposed to Google), which is extremely helpful if you work a lot in the same language pair (e.g. English-German).
If you need a more sophisticated translation tool try out
http://translate.google.com/toolkit/
This allows you to upload your own glossaries (e.g. I have my own legal terminology glossary), it memorizes your past translations, allows side by side comparison of original an translation, and indicates the progress of the translation review, etc.