A pacifier, like a diaper, is one of the ultimate signs of babification. Nothing says "I am a baby" like having a pacifier in ones mouth. There are really 2 sides to the pacifier, the business end, and the display end, I'll talk about each in turn.
The Business End
The suckling end of a pacifier is usually in one of three shapes: spherical, shapes and orthodontic. Spherical pacifiers have quite the history. A piece of cloth with coarse sugar, or even fat wrapped into it is the earliest known instance of a pacifier. There is a painting done in 1506 that shows a baby with one of these cloth teats. Now a days you only see the spherical shape on little pacifier charms that fell out of style in the 90s.
The straight nipple shape is the classic pacifier shape, more like a finger then a nipple, these pacifiers have started to fall out of favor once the orthodontic nipples hit the market, probably sometime in the 80's. You can still find one or two of these still around, Nuk, one of the primary pacifier brands that are out there. 
Finally, there is the orthodontic nipple, which is supposedly much better for babys teeth and gums. They fit the mouth a lot better as well. However, most orthodontic pacifiers are meant to go in one direction, and if they are put in upside down, they are not nearly as comfortable.
Materials
Pacifiers are mostly made out of 2 materials: Rubber and Silicone. Rubber pacifiers have a signature rubber taste to them, and after awhile, the rubber starts to get worn out and (quite literally) becomes fuzzy. Most infantilists, myself included, were raised on rubber nipples, so they are more authentic and carry a deeper fetishistic appeal then the silicone variety. That said, the taste of the silicone nipple is hardly noticeable at all. They also seem a lot stronger, and hold up to more uses then the rubber teats. It does make me wonder if in 15-20 years, there is going to be a series of silicone fetishists in the world. Will they be interested in silicon as a substance just as much as rubber fetishists are?The Display End
All pacifiers made in the last 200 or so years have a shield. The shield of the pacifier is to prevent a possible choking hazard. One of the most interesting and cool shields available is from the Nuk series, which, when the pacifier is in the baby's mouth, makes a shape like they have a wide grin; conversely, you could also see it as a heart.Earlier I mentioned that the orthodontic nipples has a particular orientation, and this is the brilliant thing about the Nuk shield. When the nipple is in the right way, the pacifier is making a smile. When the nipple is the wrong way, it is a frown! Quite ingenious.
Some pacifier shields have been taken to a new level. One in particular is a bit weird—yes, even for me—the Bling pacifier. Pacifiers, especially ones for real babies, get lost. Easily. So spending this kind of money on a pacifier like this is nothing but a self indulgent mess. Yikes.The Appeal
Having a pacifier in your mouth, is a constant reminder of ones babified state. Having a pacifier in your mouth can have a very deep pavlovian effect. Imagine the feeling of the shield against your face, the smooth nipple in your mouth, with the smell and taste of the rubber (or silicone). With A pacifier in your mouth, you can't really talk (at least not well). It is heard not to associate all that with feeing babyish.There is also a very deep relaxing/soothing about having a pacifier in your mouth. It almost begs to be sucked. Again, this probably goes back to early conditioning. The constant sucking motion again, further reinforces the soothing, babyish feeling.
Additionally, the external appearance of a pacifier is quite babyish as well. Most pacifiers (not all) are in soft pastel colors, and some even have cartoon animals on them, further reinforcing the childishness.
Of course, a blog entry about pacifiers would not be complete without at least mentioning oral fixations. So I'll mention it, and leave the rest to the reader!
