I've split this into 2 sections - the first is international (mainly US and UK based sites), and the second is for all us Aussies.

International Sites This site has so much free stuff for dogs, it'll take you a week to look through it - this has links to free samples, offers, coupons and downloads - has loads of free samples - vitamins, dog food, dog tags, a doggie bag, screensavers

dog food and dog treat manufacturers

Other good sites to get free stuff are the dog food and dog treat manufacturers. They sometimes offer free samples. You should probably check these around once a month, and most of them offer the opportunity to sign up to a newletter where they'll keep you informed of upcoming competitions and giveaways.

OptimumPet - has wallpapers, screensavers, e-cards, competitions and promotions

Pedigree - has a discussion forum, wallpapers, newsletter and promotions

Schmackos - coupon for $1 off Schmackos

Eukanuba - if you register, you can download a free bark tone for your phone, also has screensavers, e-cards and a newsletter

And for Our Aussie Friends

Here's some Australian manufacturers sites:

Supercoat - this has a free Dr Harry DVD, dog training videos and games

OptimumPet - offers a free starter pack for your dog, wallpapers and screensavers

MyDog - has e-cards, a desktop calendar, screensavers, wallpapers and dog horoscopes!

Pedigree - has e-cards, a desktop calendar, screensavers, wallpapers and games

Schmackos - has e-cards, screensavers, wallpapers and games