1. Cat Grass (dactylis glomerata)- this is an obvious one, but why spend $4 - $6 a pop at the store when you can grow it yourself? Great not only for cats to help with digestions, but for dogs, guinea pigs and bunnies, too. You can buy seeds at Sprout People.
2. Lemongrass (cymbopagon) - Kitties love the smell of lemongrass, so if you're growing some for yourself, grow some extra for them to gnaw on.
3. Catnip (nepeta cataria) - As seen in the photo below, some kitties will go absolutely crazy for this stuff. Caution: it will also attract neighborhood cats. So if you don't want it all steamrolled by chemically altered felines, you might want to grow some of it in a hanging basket. I learned this the hard way when I found all the catnip in my garden completely flattened. At least some kitties had a good time!
4. Catmint (nepeta x faassenii) - Gorgeous plant with purple blooms, attracts not only cats, but butterflies and bees, as well!
5. Mint family - Cats can be attracted to mint, while mice are deterred by peppermint. So, if you want to make your furry friends happy and lessen your chance of having a mousy gift left on your front doorstep, peppermint might be just the ticket.
6. Valerian (valeriana officinalis, valerianaceae) - Has a similar effect as catnip and is a mild stimulant. Commonly has white or pink flowers.