I'm not really sure what you're looking for in a dog, but if you've enjoyed labs but want something a little smaller, I'd start with the spaniels. Cavaliers are wonderful little dogs as are the larger spaniels found in the sporting group. Am ****ers (rhymes with Rocker if it gets bleeped out) can be delightful if you find a good breeder. The hair is purely optional. As are English (ocker spaniels and Field spaniels. I was seriously impressed with an American Water Spaniel I saw do some rally/obedience work once. Boykins look interesting, but i haven't actually seen one in the flesh. I also really like Brittanys (Brittanies?), but they are a little larger than the others I believe. Either way, I think most of those breeds are in the 18 inches or less height catagory.
Herding group in general, tends to be a bit pushy, but if you're looking for that 18 inch or less size, you may want to try the Sheltie, corgi, valhund, Pyrenean shepherd or maybe a mini Aussie (some of those mini aussies are neat little-ish dogs, some, not so much). Herding dogs are smart and born to work with their owners, but can be neurotic.
Terries, probably not what you're looking for in a dog as they have some of the same issues that basenjis do, but I think the Staffie bulls are seriously UNDER-rated as a breed. True Staffies can be hard to find and you may have breed-ban issues with them, but the several I've met are way cool little dogs.
The Toy group has been bred to be companions and they may also fit you needs, but most are considerably smaller size-wise. You would also want to look into the roots of the breed as the Group is so varied with this respect. Pug-people are just crazy about their breed, but you do have special concerns with a brachycephilic breed.
Good luck in your quest! and please let us know what you decide.