Non-Stick Cooking Pot
Most cookers have a removable ‘pot' (also referred to as a pan) where the rice is placed and cooked. A non stick coating makes cleanup incredibly easy. Rice can be sticky and hard to clean up without a coating. If you have the option, definitely choose the one with the nonstick.
Glass lid with a Hole
A glass lid is great for watching the progress of the rice. Without the see-through lid, you may be tempted to lift the lid - which is a definite no-no. A hole in the lid allows extra steam to escape without seeping out the sides of the lid (which can make a fairly big mess.)
Measurement lines
Some of the pots have calibrated lines on the inside. These are to allow you to add water without having to use a measuring cup. Most of the time you will still have to measure the rice with a special cup that comes with the cooker, but the water will be less hassle.
Steamer Tray
A rice steamer can also be used to steam vegetables. A special tray allows you to cook vegetables easily. If the cooker doesn't come with a steamer tray, you'll have to purchase one separately. Using the cooker to make vegetables is handy, you'll probably end up using it at some point. Buying a cooker that comes with one is worth looking for.
Appropriate Size
Buy one large enough to accommodate your needs, but not too large. Cooking small batches of rice in a large cooker doesn't always work well. Don't buy for those special occasions where you have a ton of people over. Buy for your daily use - perhaps a bit larger, but not too large.