Due to your current position, the fastest result other than PPC would be using product feed tools such as Google Base, which you can find at www.google.com/base
Don't forget about local marketing. Put ads in your local newspapers, host a Pet Appreciation Day at the local park, talk to vets and arrange to promote their services if they promote yours, print out fliers and get local businesses to let you leave them on their counters, hand out tons of business cards with your URL on them, donate your time to local charities but do it in the name of your business, post fliers in grocery stores and laundromats, buy a magnetic sign for your vehicle, volunteer at the animal shelter, and so on. You are only limited by your imagination.
Side note - since so many people recommended eBay to link to the store, does anyone know whether they enforce their no-linking policy? We have a store on eBay, but was informed from some colleagues that we wouldn't be able to link to our own site.
You're not allowed to link to any page selling products, either via a html link or URL watermark on an image. Having said that, it converts so well, you'd be silly not to try and get away with it. You get 3 warnings before you're forced to do a tutorial on what you can and can't do on ebay. Give it a go, get some exposure to your site, and just take the warning on the chin.