Online Dic­tio­na­ries

Oxford Advan­ced Learner's

Cam­bridge Advan­ced Learner's

Merriam-Webster Advan­ced Learner's

Learning English

BBC Learning English

VOA Learning English

Gram­mar

English as 2nd Lan­guage
A com­pre­hen­sive over­view of import­ant gram­mar points, ran­ging from begin­ner to advan­ced levels.

English Gram­mar Online
A Ger­man web­site for beginners

The English Gram­mar Book
Prac­tice your gram­mar (advan­ced level)

Voca­bu­lary

The Oxford 3000

Mer­riam Webster's 3000 words