Like I say, if you can afford better, get it. The kit lens works fine as long as you have bright daylight or other form of light. If you try taking pictures at 55mm at night in a tungsten bulb (normal incandescent) lit room of average light, you will be surprised at how slow of a shutter speed you will need to use, which results in blurred pictures. So, if you can get a better lens than do so because not only will it give you better low light hand hold ability, the constant 2.8 aperture means that much light gets to the sensor no matter what focal length you are at. This is useful because if you zoom on the kit lens, you could very easily throw your settings into the area that gives you blur. Also, the wide 2.8 aperture allows for a shallower depth of field (DOF) which gives a nice blur to things not in focus. Also, the lenses that mike mentioned are all going to be sharper at a given aperture than the kit lens; whether you care about that slight difference is up to you.
The XT is a cool camera, and like I say to everyone, if you have large hands, consider the 150 dollar battery grip. It adds a lot of mass and makes the camera feel like less of a toy, and it looks awesome.
Oh and I always recommend the 50mm 1.8. at 1.8 indoor shooting at night wont be a problem, and the super wide aperture allows for some very creative DOF usage. To add to that, the simplicity of the prime (doesn't zoom, you use your feet for that) allows an incredibly sharp picture. the canon 50mm 1.8 mkII (and all other 50's for that matter) are arguable the best bang for the buck.