Wörterbücher

Collins Reverso - German-English - Meanings by frequency in the language. Most suited for beginners.

Leo.org - German - Englisch: Comprehensive. Meanings listed alphabetically, not by frequency. Notes for technical terms.

Biolingus - From the Universität Chemnitz. Includes proverbs and sayings.

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Conjugations of Verbs and Declination of Nouns

Canoo.net
Be sure to select "Wortformen" in the menu. It will conjugate verbs and show the cases and plurals of nouns.

Verbix: Conjugate verbs.

Reverso: Verb Conjugation

German Thesauri

Openthesaurus.de

VERY COOL! A visual thesaurus: VisuelleSynonome.com: Click on image. There is also an English version if you need it!