(1) The most popular brands are Tokina, Sigma and Tamron. Some of their lenses are really good while others (especially those by Tamron) are aimed at the »value market«.
(2) So-called RAW files contain the data taken straight from the sensor and those files are camera-specific. This means that you need software which is up to date so that it understands this particular format.
Usually, the camera converts these RAW files internally into a jpg, and these jpgs are usually converted in such a way that they are ready for consumption/use. If you choose to save only the RAW files, you need to do this conversion on your computer using special software. Among the most popular choices are Aperture and Lightroom. I advise against using iPhoto, Photoshop or Photoshop Elements if you want to shoot RAW! The advantage is that you can influence the details of this RAW conversion to suit your needs. Furthermore, you can recover from certain defects, e. g. when the highlights are overblown or when the shadows are just flat black. Note that you will not be able to do miracles, but in difficult situations and with effort, you'll be able to get more pleasing results.
The downside is that RAW converters usually settle for a rather neutral look, meaning colors will tend to look less vibrant than the jpgs the camera produces. This is intentional! The reason being that the user starts from a neutral look and then makes adjustment to suit his or her taste.
Personally, I would first get familiar with the camera and all its settings (that's a pretty daunting task), and to try and nail the exposure. Getting the exposure right is key also for RAW files (the less extreme the adjustments, the better the image quality)! Then after some time (say, half a year or so), if you are interested, try to shoot RAW and then use Aperture or Lightroom to render the RAW. Note that these pieces of software are aimed at the pro market and thus, they are pretty complex.