Free downloads of audiobooks. German has the second highest number of recordings. Go to 'advanced search' and select 'German' in the 'Language' section.
WordNet® is a large lexical database of English, developed under the direction of George A. Miller (Emeritus). Nouns, verbs, adjectives and adverbs are grouped into sets of cognitive synonyms (synsets), each expressing a distinct concept. Synsets are interlinked by means of conceptual-semantic and lexical relations. The resulting network of meaningfully related words and concepts can be navigated with the browser. WordNet is also freely and publicly available for download. WordNet's structure makes it a useful tool for computational linguistics and natural language processing.
Anki is a program designed to help you remember facts / words / etc. It tracks how well you remember each fact, and uses that information to optimally schedule review times.