At one point in time (long after graduating from my university where I studied Software Engineering), I understood that I love Russian language and different facts about Russian.

Sites that help me answer the questions on Russian.SE:

• Yandex Dictionaries - search in many explanatory dictionaries, synonym dictionaries, etc.
• Russian National Corpus - has advanced options for finding word usage in texts, movies, etc. Texts are indexed starting from 1800.
• Google Ngram Viewer - Basic search for word usage in books since 1800. Good thing is that you can see the page of the book where the word or expression was found.

Other helpful sites that are picked by members of Russian.SE community: Resources for learning Russian.