Lingea Lexicon is the best dictionary out there. And not only for linux. It has very fast fuzzy search, decent interface and high-quality corpus for many languages. Where other dictionaries fail, this one is returning correct answers. I am happy user of English and German big dictionaries, but unfortunately I was not able to install it into my new 64bit Fedora 16.

Not sure what is wrong with their LD_LIBRARY_PATH setting (they distribute all required libraries along with the program), but this did the job for me:

yum install

It installs necessary 32bit libraries. I hope Lingea guys will fix that, because this product is awesome.