Ahem.

To all the non-native English speakers that write their fics in English...

I volunteer to be your editor/beta/ grammar checker.

Any genre, any paring, any AU, any rating.

Because this is painful. Really, really painful. I see a lot of stories with some real potential that kind of... lose their appeal because the grammar and spelling is too distracting.
A typo every now and then is fine; I mean... I've been speaking English all my life and I still make mistakes.
But more than 5 errors, both grammatically and spelling-wise can really dissuade readers from your otherwise very entertaining fic.