My vet recommended an enyzme toothpaste and finger toothbrush. He said the enzymes help clean the teeth the most, and the finger toothbrush is the easiest to use.
As far as I know, brushing seems to be the best thing you can do at home. Here's a good rticle about it.
http://www.healthypet.com/PetCare/PetCareArticle.aspx?art_key=e5706a99-aeea-4a61-ab79-bf8d59dd0bc9