Here are 2 I have bookmarked:
http://www.economist.com/styleguide/introduction
http://www.guardian.co.uk/styleguide/a
Please post any you use.
'Life shrinks and expands in relation to ones courage'Anais Nin
Split Infinitive
The English-speaking world may be divided into (1) those who neither know nor care what a split infinitive is; (2) those who do not know, but care very much; (3) those who know and condemn; (4) those who know and approve; and (5) those who know and distinguish. . . . Those who neither know nor care are the vast majority, and are a happy folk, to be envied by the minority classes.