I'm hooked on the ninjaword FARR plugin! 

Sorry folks, my images won't attach properly.

I like their little games for example "match up". It's a fun way to expand knowlede.

I wish there was something like this for German as well.

The dictionaries I use most often are those that translate from various languages into English and vice versa.  And far and away, the best online (or offline) set of dictionaries I know for this are those offered for free at WordReference.com.  The site offers dictionaries in a number of different languages, but I tend to use those for Spanish most often.  What I love about the WordReference dictionaries is that at the end of each entry, they include links to discussions of that word or phrase in the WordReference.com forums.  You thus get a much more nuanced idea of what the word means, how it's used, where it's used or not used, etc. etc.  It's an amazing resource!  

I know the world is full of fantastic dictionaries etcetera, but it is so easy (and common) for me to merely Ctrl+RightClick and see the result at once in Babylon, that I almost never will search another place.

Curt, I almost started my message (right above yours) by saying that the first place I generally turn for translating to/from English is Babylon.  I didn't say that because 1) I interpreted the original message as asking about online resources, and 2) when I want to get an even better sense of which word to use and why, I'll turn to WordReference.com.  It covers many words and expressions that Babylon omits, and it often offers more nuanced information about usage.  But I agree that Babylon is terrific.

someone should mention babylon dictionary too 

Did someone author a script for Firefox, for 'Google Define'? 

-thanks a lot, daddy! 

You can easily add a "search engine" to firefox for almost every site that has a search form: just right-click into the search field and select "Add a Keyword for this search...", give it a name and a (preferably short) keyword.

Now you can type "<keyword> <search query>" in the address bar and firefox will open the search results of that site. I use it frequently for dict.cc and wikipedia, where this approach works very well. Search forms that are submitted by POST are harder or impossible to use this way.

True, that's quicker and I should have mentioned that. Lately I've had a preference for having each search available as both a search plugins and a keyword because of certain add-ons that work only with the search plugins. One disadvantage of this is that sometimes I have to create the search plugin myself, like I did for DonationCoder.