Orbital sanders, also called finish sanders, are primarily used to smooth surfaces between finish coats. But an orbital sander can be used for much more. The fast and tight orbiting movements make the the orbital sander capable of aggressively smoothing wood.
You have two types of orbital sanders, the palm sander and the two-handed sander. The palm sander is compact, ideal for for smoothing interior surfaces in confined spaces. The two-handed orbital sander is larger and more powerful, it can be used for a number of sanding tasks. Note that the orbital sander has a tendency to leave swirl marks. You need to be careful when using a finishing sander. If necessary, use a sanding block to remove swirl marks.
Here are our recommended orbital sanders:
Best Palm Orbital Sander: Makita BO4556K 2.0 Amp 4-1/2-Inch Finishing Sander
Our Rating: 4.5/5 
The Makita BO4556K Finishing Sander is an excellent palm sander. Despite the small size and light weight, it is powerful. It generated very little vibrations and the dust collection is very good. It is comfortable to use. If you are looking for the best palm sander, here it is. You get a hard case with the Makita BO4556K. Thanks to the low price, you get excellent value for your money. At Amazon.com can learn more about the Makita BO4556K 2.0 Amp 4-1/2-Inch Finishing Sander.
Best Value For The Money Orbital Sander: WEN 6313 Electric 1/3 Sheet Sander
Our Rating: 4/5 
If you need a cheap sander, then the WEN 6313 Sheet Sander is worth having a closer look at. It may not be the best sanders on the market, but it is capable of handling everything that can be expected of a sheet sander. The price is certainly very attractive. The cheap price means that you get very good value for your money. It is not a sander for professionals but for the occasional sanding task it is a very cost-effective solution. At Amazon.com you can learn more about the WEN 6313 Electric 1/3 Sheet Sander.
Best Two-Handed Orbital Sander: Bosch OS50VC 1/2-Sheet Orbital Finishing Sander
Our Rating: 4.5/5
Often, buying a random orbit sander is better than buying a two-handed orbital sander. But if you want an excellent orbital sander, the Bosch OS50VC 1/2-Sheet Finishing Sander is the sander for you. Note that you can remove the front handle if you are going to use the sander in tight spots. The Bosch OS50VC sander is very quiet and generates very little vibrations. The dust collection is very good, but you probably need an adapter if you want to connect it to your shop-vac. Bosch OS50VC is expensive but you get what you pay for, an excellent orbital sander. At Amazon.com you can learn more about the Bosch OS50VC 1/2-Sheet Finishing Sander.