Vocabulary

http://www.bbc.co.uk/worldservice/learningenglish/youmeus/quiznet/archive.shtml

Dictionaries

Monolingual :
http://www.ldoceonline.com/
Monolingual and bilingual:
http://www.wordreference.com/

verbal tenses

1.present perfect
2.-present perfect 2
3.-present perfect 3
4.-present perfect 4
5.-present perfect 5
6.-present simple versus present continuous
7.-present simple and continuous 2