If you do fine carpentry, say making furniture or cabinets, you probably have need to do sanding of fine details and hard to reach corners. If so, you might just need a detail sander, which is power sander specially designed for sanding small details. These can save you a lot of time while still giving you a great sanded finish.
Detail sanders are available either in corded or cordless models. The cordless models are easier to handle, but of course, you want to make sure you choose a model with enough power. You might also want to purchase a spare battery so that your can keep working when the first battery runs out. Corded models tend to be cheaper, and have more power. I personally prefer cordless tools, but the choice is yours.
Sander Orbital
As with any power tool, it takes some practice to really get the hang of using an orbital sander correctly. So, make sure you have a good handle on using the tool before using it on a real project. You don't want to ruin that piece you've worked so hard on.
Detail sanders are available from the manufacturers you've probably heard of, such as Bosch, Porter Cable, Ryobi, Triangle, Dewalt and Versapak. We all have our favorite brands, but do some research online to see which one is best for you. One thing to keep in mind, if you do go for a cordless detail sander, is that you might want to match the brand of any existing cordless tool that you own, so that you can share the batteries. Not all batteries are sharable, but many cordless tools systems, like Ryobi, are designed with interchangeable batteries.