Tis the Season! Dining Room Centerpieces

I was walking through AC Moore the other day in search of a great frame (found!) and the sales staff was putting out the autumn themed items.  Yikes.  Then I turned a corner and there were... POINSETTIAS!  Seriously?!  It's August, at least leave it until after you take down the back to school gear (which also gives me the shakes).  But, this got me thinking about centerpieces again.  I just cannot stop thinking about the limitless options for my underused dining room.  Here's my most recent iteration - more on that here.

I thought I would share my friend Amie's awesome summer dining room centerpiece for additional inspiration.

I love that table runner and the wicker chargers, but the shells make the table.  I have a feeling that the shells we have collected this summer won't be as pretty as this Pottery Barn collection, but we will have the memories.

What do you do with the shells or other vacation mementos that you collect on your travels?