If you want really dry, perfectly separate and elongated grains with a rice cooker, I'd suggest this method which gives me excellent results. It is a bit more work (and requires another pot), but works well with basmati/long-grain rice and any rice cooker with a steaming basket.
- Rinse your rice either in a collander or by putting it in a saucepan and swirling/changing the water a few times
- Leave to soak for 20 minutes
- Bring to the boil, boil for 2 minutes, meanwhile boil a kettle of water
- Drain, and rinse in boiled rice in cold water and allow to drain thoroughly
- Add the boiling water from the kettle to the base of your rice cooker
- Place the rice in the steamer section (you may need a sheet of kitchen towel to stop the rice falling through) and place in cooker
- Steam for 15 minutes once steam emerges through the rice
The problem with many rice cookers I've come across is the way they actually cook the rice. When the rice and water are added, the combined weight pushes down on a switch and brings the water to the boil. Once the water has evaporated, the cooker goes into "keep warm" mode, which ends up with congealed rice at the bottom.
You might get better results by just soaking/rinsing the rice beforehand or adjusting the water quantity downward, but from personal experience I've never managed to get absolutely perfect rice that way. Different brands of rice will also behave differently.