Why is the bell, well, bell shaped? What is the significance about the bell shape, when its hit at the rim it rings/produces sound better than other shaped objects? If so could anyone explain a little bit on it.
EDIT: From the suggestions in the comments, clarification for the term "sound better": Sound more effective for the purpose which bells are created for. (Thanks Justin)
 A: A completely missed part of the answers so far has to do with acoustic matching.  We hear sounds that are waves in the air;  sounds that we hear are created by vibrating systems and materials, and those vibrations must get efficiently transferred to the air for us to hear them.  The shape of brass musical instruments like trumpets, trombones and tubas is "bell shaped" so the standing vibrations that are created inside the instrument get efficiently matched to the acoustic impedance of the air. We can create those same sounds in long straight tubes, but they would not get efficiently transferred into the air outside of the tube.
A large church bell, when it is struck, has internal vibrations in the bell's materials that initially get transferred to the air inside the bell, and then, because the bell is "bell shaped", get most efficiently transferred out into the surrounding air, making the sound we hear to be "loud".
A: The bell is typically bell-shaped for two reasons, first because the circle is structurally strong and this allows bells to be struck with greater force than if the shape was flat or had sharp edges which would be more prone to cracking, further the circular shape allows a wave to travel around the bells perimeter so that standing waves can develop around the circumference of the bell. It is the resonance from standing waves that is responsible for the sound of the ringing. 
And second the bell's shape makes the timbre of the bell more musically pleasing. The reason for the increasing diameter as you go from the top to the bottom of the bell is so that the bell resonates at different frequencies which can be tuned in a large bell so that you have what amounts to a complex musical chord playing when the bell is struck.
For example, a given bell might have a resonance at the fundamental, a subharmonic one octave lower, a minor third above, a fifth above, and a full octave above. The different diameter sections of the bell contribute to these different harmonics.
Bell construction is as much an art as a science. Here is a good online resource that describes the process of creating a large bell:
https://www.msu.edu/~carillon/batmbook/chapter4.htm
also the next chapter which goes deeper into the acoustics of bells:
https://www.msu.edu/~carillon/batmbook/chapter5.htm
A: The correct answer is the following: bells have the shape they have because they are made to be hung in high places. The shape focuses sound downwards and maximises loudness.
This has a cost. The shape is not favourable to hold a steady pitch, and they sound much worse than tubular bells, which are used in symphony orchestras because of their clear and precise sound, which is obviously a more important requirement in that context.
Japanese bells have cylindrical shapes, too.
Finally, cow bells have yet a different oval-like shape probably because of the ease of production. They don't sound very well at all, they are more percussive than melodic.

As a side note. The argument in another answer about harmony is quite wrong. First of all basically any musical interment produces harmonics. That is the fundamental reason why different instruments have different timbres. So, sure, it would apply to bells too (with the caveat that church bells don't have a constant pitch) but it is not specific at all to bells or to their choice of shape in particular. For example the material with which a bell is wrought is just as important.
A: Bells have evolved into the "bell" shape because a vibrating bell produces different partial frequencies depending on metallic thickness and shape. My source says that "The shape of the bell has evolved so that the main partials are in roughly the right relationship. Removing small amounts of metal from different parts of the inside of the bell adjusts the different frequencies. A modern bell is cast deliberately thick, and then tuned on a vertical boring machine (a giant lathe). Before this, metal was chipped away with a tuning hammer, a practice that persisted into the early 20th century, despite the introduction of tuning machines from the late 18th century."
In some bells, the tuning is done by stripping inner annular rings from the bell. Obviously this is much easier than trying to remove the proper amt of metal from other shapes.
Thanks for an interesting question :)
A: uhm .. so you can hangup something inside and have it hit the walls?
if you want a sound and you hit it from the outside, i doesn't need to be bell shaped.
consider a "gong".
also bells are /  were expensive to manufacture during a certain time and used for religious purposes. it is easier to "cast" a huge sounding object in a bell shape rather then as, a tube or pipe?
furthermore also,you can hang a bell in a way, as opposed to a "gong", in a way so it doesn't need an army of men to operate and make much noise. one novice hanging on to the rope will suffice.
