Purdue Online Writing Lab

Purdue Online Writing Lab - I've not checked it out fully, but it looks like a great resource for high school and university students.

English Grammar 101

English Grammar 101 - some free grammar lessons

Daily Grammar

Daily Grammar - free lessons for ages 10 and up

Grammar Bytes!

"Grammar instruction with attitude"

Writing Fun

Writing Fun - "Writing Fun explains the types of text commonly written in schools with student examples showing text structures, grammatical features and publishing ideas."

FactMonster's Writing Skills site

For kids: learn different types of writing as well as spelling and grammar.

On or By accident

Ok, this is somewhat educational, but more amusing than anything:

http://grammar.quickanddirtytips.com/on-accident-versus-by-accident.aspx