I definitely recommend a tablet! It really helps improve you. But like some said above, they're not for everyone.
Sadly, most tablets are expensive. The lowest priced Wacom tablet's like, $70. But they're really, really good quality and last a pretty darn long time if you take care of it. These are what most people have. Don't let the fancy-schmancy versions of the Bamboo tablets fool you. You probably don't need the wireless tablet (unless you're actually in that situation, but Wacom provides you with the fucking LONGEST USB cable you'll ever see), nor do you need the touch version. The wired / pen only version's all you'll need.
But there are also cheaper tablets. Specifically, a Monoprice tablet is perfect for a tight budget. I hear that it's pretty good quality, too. So definitely look into those. I can't give you an opinion on them as I've never used one.
But of course, if you have the cash, definitely consider getting an Intuos or a Cintiq. I often hear that Cintiqs improve your art and make drawing / animation a LOT easier and faster. But they cost like, $1k, so it's out of most people's price range.