Gift for Preceptors? What do you think?

I will be coming off an 8 week unit orientation in two weeks. During this time I have had three preceptors who have all been helpful in teaching and exposing me to the processes and procedures that are likely (and less likely but important to know) that occur on the unit. As a new grad my preceptors have helped to build my confidence and made me feel comfortable on the unit. So my question is: is it appropriate to buy them each an individual gift as a thank you present? Might this look bad to the other nurses on the unit? Is a thank you card enough? I definitely do not want to 'rock the boat' in any way but I would like to show my appreciation for the time and effort they gave in teaching me.
I think a small token of your appreciation would be great!

a nice card with a Starbucks gift card inside would be nice, and not obvious...or a gift card of anything you choose...