As a Canadian living in Berlin, I'm constantly learning German, and the best resource is a good dictionary. Paul Hemetsberger's dict.cc is not only the best online English-German dictionary I've found, it's one of the best examples of how an online resource should act. Even if you have no interest in learning German, it's worth having a look just to see what makes a great site.
This site is optimized for people who will be using it regularly. You can click on 'Remove Ads' which will hide all the ads until you close the browser. You can also click on some section titles to hide the sections you don't need, which cleans up the interface, and these preferences are remembered using cookies.
There are simple features that make the site even easier. Alt+S will put the cursor into the search box, which is very handy when you need to do multiple searches. You can simply enter the URL dict.cc/word to automatically search a word (I wish Google would do this!). There is even a slimmed down "pocket" version at pocket.dict.cc, which has become the only web site I actually use on my cell phone.
Everything in the results is clickable. You can click on a single word to look up that word, double-click a table cell to look up the whole phrase, or click on a drop-down menu beside each result to reveal a number of options. You can hear a spoken sample of the word or phrase, which doesn't launch a popup or make you save an mp3 - it just plays instantly using Flash. There are also links to the word in the other popular online dictionaries, in case you aren't satisfied with the results or want more details.
The site is built on contributions from users. This means that the dictionary is as up-to-date and complete as possible. For me, this is very important - I want as many alternative translations as possible to understand the different ways German words can be used. Anyone can suggest a translation or correct an existing translation, and all changes go through user-based moderation. And since the data is user-contributed, the author Paul doesn't claim ownership to the word list. It is available for download as a text file.
There are tons of other cool little features all over the site, too many to go into here. You'll have to play around with it yourself.