LEDs are really not bright enough (yet) to be the sole lighting source in a room. To boost percieved brightness, most manufacturers are putting quite narrow lenses on the front which gives a narrow beam and makes lighting a bit patchy.

The best LED technology available at the moment are some 1W Luxeon lamps available in a variety of fittings. They can be retro-fitted to replace lamps such as 50mm low voltage dichroics (will work off the standard transformer), mains GU10/GZ10 or even old reflector type mains screw type lamps. They are bright, you're looking at near a 20w low voltage lamp. But just like Tahir said, the colour temperature is quite cool in the White option, and the beam is very narrow. These are best as decorative or accent lighting really and they are also available in the primary colours and orange too. These lamps are not dimmable. Dimmable LEDs require some control gear, and you are looking at a significant amount of money for that. They are rated at about 30,000 hours life.

Its good that flourescent lighting was also mentioned. Flourescent technology is getting smaller and brighter all the time and there are quite a few interesting lamps available. Megaman do have some great products, including dimmable compact lamps. I would absolutely recommend taking a look at fitting some interesting flourescents to save some energy. They are bright, come in comfortable colour temperatures and have a long lamp life if you go with a reputable brand. The price/light_output/energy_usage ratio is a lot better with these.