The 50 mm f/1.4 is supposed to be a fantastic lens. The 50 f/1.8 is also very good, and it's half the price. You may want to go to a store and ask them to put one of these lenses on a camera for you before you buy it. Take a few photos, even of the salesperson and notice how blurred the background is (that's a good thing).
Prime lenses are generally sharper and have less problems with vignetting, chromatic abberation (Google these terms if you need to), etc, because prime lenses like the 50 mm f/1.4 and f/1.8 only have one focal length and so a have minimal number of moving parts.
It's also fantastic for taking shots in low light situations, like in a house at nighttime. The 28-105 mm f/2.8 is probably fantastic, but it's not going to be nearly as good in low light when compared to a f/1.4.
However, if you really want to have fun, the 50 mm f/1.4 might not be the lens to get since you want closeups and portraits.
An 85 mm f/1.8 or f/1.4 is excellent for portraits, as is a 100 mm f/2.8 macro lens. This would allow you to shoot good portraits and shoot things from very VERY close up if necessary (ie: small bugs, etc).
