Have you looked at the Cutting Edge series? It is used by a lot of language schools around the world, and whilst not being completely neutral in terms of culture, it does not preach a particular culture. What it does do, in relevant chapters, is to ask students to reflect on cultural differences.
Here is a link to the webpage: Cutting Edge
However, for the younger students, try the following: Longman English Language Teaching Catalogue - Course
Both series are published by Longman Pearson and their website will allow you to look at examples and possibly even print a chapter so that you can give it a go.
Otherwise, if you have the inclination, you could just get a copy of Practical English Usage and create your own activities using the information from the book as it covers almost every conceivable aspect of English relevant to learners.
Back to cultural neutrality, I think that most of the courses available are culturally bias at least in the fact that they espouse a communicative approach to learning as opposed to a proscriptive approach.
I am sorry that I cannot be of more help, but I have not taugh general English for a while now.
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