A short list of online reference databases covering encyclopaedias, dictionaries, thesauri and almanacs:
Dictionaries: You will find many specialist dictionaries on a wide range of subjects in Oxford Reference and Credo Reference, as well as the Oxford English Dictionary, the definitive English language dictionary.
Thesauri: A thesaurus gives lists of alternative and opposite words which can be useful in writing assignments. You will find one in Oxford Reference and Oxford Dictionaries. Find quotations in both Credo Reference and Oxford Reference.
Encyclopaedias: Apart from the well known Encyclopaedia Britannica there are many specialist encyclopaedias in Oxford Reference and Credo Reference, for example the Encyclopedia of Mammals in Oxford Reference and Encyclopedia of Urban Legends in Credo Reference.