One nice thing about baking bread is that it costs almost nothing. Sure, if you want to you can spend hundreds of dollars on a mixer, fancy pans, baking stones, and other things, but a good baker can turn out excellent bread with two bucks of ingredients and an old cookie sheet.
There is only one thing, aside from a couple of good bread books, that I've bought for baking bread that I really value: an instant-read thermometer.
Why is an instant-read thermometer so valuable? Because I am lazy. And incompetent. And if I can find a way to avoid using my brain, I will use it.
Really though, the reason one is so useful is that the simplest way to tell when your loaf is done is to check the temperature in the center of it. Soft, pillow breads that contain fats are done baking when the internal temperature is around 180-190 degrees. Drier, crusty breads need to bake until they are between 200-210 degrees inside. Simply poke the thermometer into the bottom center of the loaf and in thirty seconds you should have an accurate read of its internal temperature.
Tapping the loaf and listening for a hollow sound is a tried and true method of checking when a loaf is baked, but it is definitely more of an art than a science. Being the geek that I am, I love having a simple, reliable way of knowing when my loaf is done.
A lot of folks may already have an instant-read thermometer around their kitchen. They come in all kinds of fancy shapes and styles. You can easily spend more than seven bucks on one if you want to, but I don't see the necessity of doing so.