This website is an exceptionally good reference tool for verbs. You can quickly look up charts for all verb forms and tenses.

This online dictionary provides the usual range of tools: definitions, audio files for pronunciation, etc. Its example sentences are provided by the Goethe Institute and can be very helpful for determining the finer meanings of a given term.

LEO is another good online dictionary. This particular site has helpful chat forums for advanced students seeking to understand conversational form or antiquated terms.

Linguee searches the Internet for terms and seeks out reliable sources for real-text bilingual examples (i.e., university, medical, and international business websites). This website can be another helpful tool for determining appropriate usage of an unfamiliar or new term.

Index to many dictionaries. Be sure to choose "Find translation." Search engine to words more than a dictionary

Google's machine translator

Machine translator (does not catch all nuances)