I have two ideas for you, both of which our family does and really enjoys. First is we have a "blessing cup". This is a really pretty goblet-type glass that we decorate with a pretty ribbon and fill with sparkling grape juice (no one in our family drinks alcohol, and this also makes it kid-friendly). We pass the cup around the table at the beginning of dinner and everyone says what they are thankful for that year and takes a drink then passes it to the next person and so on. It's great to hear the different responses between the grandparents all the way down to the toddlers!
The other thing we do is at Christmas, but you could use it anytime your family is all together. We bought some nice white tablecloths and fabric pens/markers and every year everyone writes what they are thankful for on the tablecloth with the year, and then we add to it each year. This is great because each year when we bring it out we can look back on what has been written in the past and talk (and sometimes laugh!) about where we are now in our lives.
Whatever you do I hope it can be a tradition your family enjoys from year to year! I grew up in Texas and now am here - welcome to Michigan!