I voted twice a year, I think that would be about average but I am not quite sure.
I only give a bath when they need it. Sometimes I only give partial baths (like Kaige's butt baths when he has the runs).
Raustyk & Kaige get a bath more often as they get into yucky things more often than Nanook. That and it is hard for Nanook to stand for that long.

As far as shampoo goes, I keep a variety.
Currently in my cupboard I have:
Lambert Kay, Fresh N Clean, Oatmeal and Baking Soda (LOVE the stuff)
Variety of Four Paws shampoos, Magic Coat Fresh Essence, Coat Pet Shampoo for White Coats
Variety of 8in1 shampoos, Perfect Coat Black Pearl, Perfect Coat Natural Oatmeal

I also have some conditioners & cream rinses but the brand names are all unkown, I always get them from vendors at dog shows.