1) Wordreference (http://www.wordreference.com/):
It is a very good dictionary with a lot of explanations in different contexts. You can also look for expressions and the conjugation of verbs and there is a forum to ask any questions you might have. I'm using also the app and it's very useful. And you have a lot of languages.
2) Linguee (http://www.linguee.com/english-german):
This one is very useful if you want to look for a complete sentence, expression or word included in different texts where you can verify in which situation could you say it properly.
3) Reverso (http://diccionario.reverso.net/):
I use it normally to verify the conjugations and you have also the dictionary and other options in different languages.
4) I have also been told that Pons (http://es.pons.com/traducci%C3%B3n
) is very good for German.