UltraLingua is a very complete dictionary and translation tool. There are quite a few different applications available by UltraLingua. For testing, I downloaded the first one listed on their website, which happened to be the English Dictionary and Thesaurus. This is a single-language tool, but there are multi-language dictionaries available.
UltraLingua consists of a main window from where you can access all of the programs features. There, you can simply click on the search field and type a word, and you will be taken to the dictionary part of the suite. The search field finds results as you type them, which makes it easy to find similar words and to make sure you don't miss-spell a word. The dictionary is very complete and descriptions are good. I found all the words I tested it with.
The rest of the features are very interesting. Under the "Dictionary" group, you will find the Conjugations and Numbers features. These allow you to conjugate any verb and to quickly convert numbers to text. Under "Tools", I like the Flashcards feature, which allows you to create virtual flashcards with words and their meanings.
All in all, this is a nice dictionary with some interesting extra features. The trial is full-featured and it lasts for 9 days.