Two small dogs, one 8 years one 16 months - essentially they both just get fish oil. I've used probiotics in the past for a brief period when we've had stomach issues with one or the other of them, but other than that nothing besides their staple diet.
I have a 2 year old hound mix. The only thing I currently give him is salmon oil. I thought about getting him started on a light dose of glucosamine, but after some thought I've decided to wait. I just want to keep things simple for now.