Supplements are great, a good addition to a high quality kibble - what are you feeding, btw?
I use one that specifically contains what I need for my guys: multi vit/mineral, probiotics, EFAs (ess. fatty acids), and digestive enzymes. It is this one:
http://www.onlynaturalpet.com/produc...at/999065.aspx
I also give Calcium, but that's bc I home cook, otherwise you don't really need to supplement calcium.