This is actually a very important matter -- perhaps we who have been born Christian have never thought about "is Christ God", but as we grow in the Faith and ponder on His word and His life to ME it seems clear that He could only be God or a madman, nothing in-between, not a super-angel, not a prophet
Very good point Cronos, eze and CYC have presented their case without hostility and we should be at all times ready to give a defense for the hope that is within us. While I agree with Cronos that it seems self-evident that Jesus can only be either God, a liar or a complete lunatic, we still should provide evidence of why that seems self-evident to us and why rejection of Christ's deity is a heresy that all Christians rightly condemn.
Let's begin with the basics. Christ Himself makes the claim to deity, stating in John 8:58 that "Before Abraham was, I am." which, as may or may not be readily known, is a direct claim on His part to be "I AM". For reference, this is the same name that Yahweh told Moses to tell the Children of Israel when they asked who had sent Moses to them. Exodus 3:14 for reference.
Exd 3:14 KJV - [14] And God said unto Moses, I AM THAT I AM : and he said, Thus shalt thou say unto the children of Israel, I AM hath sent me unto you.
You will note from the rest of the text in John 8 that the Jews immediately recognized this as a claim to deity due to the fact that they attempted to stone him for blasphemy as soon as they heard this.
Continuing on, again in Mark 14:61-62 we see Jesus claim to be deity and the Jews' reaction to that claim. They understood that He was claiming to be Yahweh. Again, the verse for reference.
Mar 14:61-62 KJV - [61] But he held his peace, and answered nothing. Again the high priest asked him, and said unto him, Art thou the Christ, the Son of the Blessed? [62] And Jesus said, I am: and ye shall see the Son of man sitting on the right hand of power, and coming in the clouds of heaven.
There is, of course, more evidence for Christ's deity but this should be enough to at the very least get the conversation started properly.