I've used a Weber Smokey Mountain (aka Weber Bullet) for years. Its gives great results, holds a lot of meat, and is not terribly expensive. It takes a while to get good at it, but there's lots of online resources. Alternatively, there are a lot of electronic peripheral devices that will basically guarantee a consistent result.
I've also had great results with the Big Green Egg (which is more versatile, as it will cook at high temperatures). However, if I were to upgrade, I'd get one of these:
Yoder Smokers | Pellet Grills