RAW or JPEG, the two serious choices for camera lovers. It is really the first question you must ask yourself when you get your DSLR.
Lets talk about both before we decide witch one to go with.
When you use JPEG the files are processed in the camera according to the settings on your camera. Which in many cases is fine, if you have the right settings for the photo. That means you have to be more careful with your exposer and white balance. When you open the JPEG image in a computer the data has already been saved in this format, reducing your options when it comes time to edit.
RAW files are uncompressed data right out of the camera and is the best form of digital capture. So with raw you are able to go in and edit a more detailed picture and get much better results then if you took a JPEG image. My only downside with RAW is converting them to JPEG after but its nothing to worry about really.
If you have the space for it I would shoot in both, RAW+JPEG, if you camera allows it. This will take up more space but when you get done with a shoot you can either take the smaller JPEG images or you can go and edit the RAW.
My deciding factor, RAW is the way to go, if you get a few more memory cards then you'll never have to worry about how much space the images are taking.