What to look for when buying a rice cooker?
Volume

Volume is usually the primarily advertised statistic for rice cookers. This indicates the volume of cooked rice that can be prepared in one cycle. Common sizes include 5.5 cups and 10 cups. 5.5 cups is completely adequate for a family of five people for a single meal. 

Bowl quality

Bowls in entry-level models are typically aluminum. Higher end models will be stainless steel. The same heating properties present in pans are relevant here. Aluminum heats quickly, and unevenly. Steel provides a more even heat.

Also of concern is the interior of the bowl. Nearly all bowls have a non-stick coating of varying quality. I've seen the coating start to flake off within a handful of uses on the cheaper rice makers. Higher end bowls can have a durable coating that lasts years or longer.

Cooking logic

The simplest and cheapest rice makers will have basic static logic. You put rice in, push a button, and the logic simply applies X amount of heat for Y minutes.

Higher end models also have additional functions including:


Presets for multiple varieties of rice
Delayed/scheduled cooking (like a slow cooker)
Keep warm functionality 
Digital displays
Elapsed/remaining time displayed
Dynamic monitoring and adjustment of temperature/humidity 


Cooking/Heating method

Most rice makers use a simple coiled electric heating element located under the bowl. This is a major cause of overcooked/browned/burnt parts where the rice contacts the heated area. This is exacerbated by cheaper aluminum bowls.

Higher end rice makers use induction heating. Induction is a rapidly alternating magnetic field which uses the entire bowl as the heating element. This heats much more evenly and is far less likely (almost impossible) to burn the rice.

The highest end rice makers add pressure cooking capabilities. Pressure cooked rice purportedly is softer, and retains softness longer than regular cooked rice.

Brand &amp; price

This is probably the most important. In my experience, you actually get what you pay for. Without fail every American brand rice maker (presumably made in China)  I've used has been atrocious. The most positive thing I can say about one is "it worked great for the first batch".

There is one Japanese manufacturer that stands out from the pack: Zojirushi. I cannot overstate how amazing their product is. It literally just works, every time. I received the Zojirushi NP-HBC10 5-1/2-Cup Rice Cooker and Warmer with Induction Heating System as a gift over two years ago. I have used the hell out of this thing and have never had a less than perfect batch of rice.