Hi Tim - here's what i've done in the past. what (do you send them a gift basket? something more personal) - be careful with food allergies etc, especially for entire family
why (just because it's the holidays? because they're amazing and this season is about giving?) - I chose to sent something at the first of the year, and focusing on the partnership we've created and what we can look forward too for the new year (or more)
how (tied into the what - is there a way to make it more exciting than traditional gift giving?) - this was mostly to say thank you for being a valued member and partner with us, etc