Here is a list of companies or brands that have dairy-free options (either dedicated or just a few things in their product lines). It is not all-encompassing, nor is it meant to imply some endorsement by me (though I do use products from most of these places, and wouldn't use what I don't like), and I'm not being paid to advertise them. As always, read the labels before eating something, and your mileage may vary.
Alexia - frozen products that often do not contain dairy
Alternative Baking Company - dairy-free cookies
Cherrybrook Kitchen - allergen-friendly cake, cookie, brownie, frosting, and breakfast mixes
Go Max Go - dairy-free alternatives to mainstream candy bars
Kinnikinnick Foods - dairy-free baked goods
Silk - dairy-free soy milk, yogurt, and creamer
Tofutti - dairy-free frozen treats, cream cheese, sour cream, and cheese
You may also want to consult Go Dairy Free for a list of resources and recipes, but they'll make you pay for 'em.