As well as proving the oneness of god through the Quran, logic too can help prove this as I shall explain. If you ask a believer in god, whether he believes in one god or ten, you will probably find that somewhere in his definition of the term 'God' he rules out the possibility of god being weak, inferior or compromising. From this, we may say that something that is weak, inferior or compromising cannot be a God. Yet the very fact that there is more than one god suggests two contradictory possibilities; That the Gods are of equal power and therefore are compromising, or that their power is uneven resulting in some Gods being inferior to others. From this ontological argument one can conclude that there can only be one true god.
Zoroastrianism- the mainly Greek belief that refers to the belief that there are two gods- one evil and one good- on account of the reasoning that I have mentioned can clearly be put aside. However one can also add that if there was one good god and one evil god, or even any other form of polytheism, the world would be in chaos and thus the order of the world would break down. Logically, by the use of the common analogy that one can not have more than one captain in a boat you can start to see the reasoning that I am trying to convey. With power in the hands of more than one god there would clearly be argument. However, one effective point that non-Muslims or curious ones such as myself put across is that this theory is contradictory to Islamic teachings, because we are associating god with the human attribute of not being able to share power. The answer to this is clear. It is not an assumption by humans that there would be chaos if there was more than one god, for if it was -putting in mind that Islam teaches that humans with their finite perceptions cannot make any assumptions about God- than it would be very wrong. However it is a fact made known to us by Allah Himself in the Quran:
"If there had been in them (the heaven and the earth) other gods beside Allah, then surely both would have gone to ruin." 21:23
Pantheism is another theory that Muslims believe to be wrong. Although Muslims believe that Allah is everywhere, he is a separate entity and therefore cannot be reincarnated in everything as the pantheists believe - who although are not strictly defined as polytheists, they are certainly not monotheistic in the Islamic sense.
Going against the oneness of Allah, Shirk, is a very major sin:
"Surely Allah will not forgive that any partner be associated with him" Holy Quran 4:49
Regarding the attributes of Allah, Islam teaches that Allah although He has many attributes, cannot be fully understood by man. Man is restricted in thought into that which is manifest, Allah however is unique and above human manifestation.
Allah, the god of all humanity, is perceived differently in other religions. Since man would be limiting Allah by creating a physical image of Him Muslims do not. Allah is as I said unique and superior to His creations. Thus the biblical statement that was mentioned in Genesis Ch1 v27 that God has created man in his own image is a view that is not shared by Muslims.
Other religions believe that God resembles creation- they believe in describing causes by their effects. An example of this is that we can describe a corpse to be horrifying (the effect) but we may also say that the person responsible for this death, the murderer, (the cause) is also horrifying - cause resembles effect. This theory can easily be put aside, for although it may be true for a limited number of examples, the vast majority can prove it wrong, i.e. a shoe does not resemble a shoe maker, etc.
Thus Islam does not try in anyway to personify Allah. Whilst it may be true that two of His attributes are that He 'Sees' and 'Hears', this does not mean that He has eyes and ears like you and I, His hearing or seeing cannot be comprehended by us as finite beings.