I feed mine high-quality lab blocks 24/7. Boring but convenient and functional.
I suppliment with Small World Vitality Suppliment, which is a pelleted diet with vitamins and natural ingredients. It's got all sorts of beneficial bacteria and probiotics, and has anise extract (licorice) which seems to really be helping, among my other tactics, to keep their urine odor down to a minimum. They really like it, and I feed a tablespoon to each colony every other day.
Here's the link to it at Petsmart:
http://www.petsmart.com/global/prod...T<>prd_id=845524441808059&bmUID=1103606692009
(for some reason the forum won't let me do URL's?)
And once a week each colony gets Vitakraft Yogurt Drops, one per mouse. The regular flavored ones, they don't like the berry flavored ones.
The suppliments with the probiotics seem to really aid in their digestion, and they don't seem to waste as much food and they're looking really good with clean and shiny coats. The babies they've had ever since I started have been nice and chubby, and even the once-ragged and newly-separated weanlings are looking good.
I don't feed seed based diets, they seem to develop a taste for them and then don't want anything else. Besides, all seeds are is fat and maybe a few minor trace elements. But to each their own I suppose. Whatever works for one, doesn't have to work for us all. =)