As I write many emails for my job, in these days I have to put at the end some greetings. I am using something like these:
I wish you a great 2009
I hope you a brilliant new year full of customers (when I write to shops)
I hope you have had a good Christmas (at the begging of the email)
Are they correct?
When you send messages to shops and/or other businesses, you could say
I wish you a prosperous new year.
This is much the same as wishing them 'many new customers'.
In your messages, you can also say, I hope your holidays have been bright (or happy, or full of joy or...). This word (holidays) applies to all the festive/religious/cultural events of the winter season, not just the Christian ones.
Wishing you happiness and peace in the new year,