http://www.azargrammar.com/

[if need of some grammar practise this site shall not be overlooked ... pdf or doc files available, and much more]

http://grammar.ccc.commnet.edu/grammar/

[practise, practise, practise ... ]

http://www.grammarbook.com/

[title says it all]

http://www.ucl.ac.uk/internet-grammar/

[and some more, especially for those striving for theory]