punctuate the sentence

There are two possible ways to punctuate this sentence, with and without the serial (Oxford) comma.

I came, I saw, and I conquered. (Oxford comma)

I came, I saw and I conqueued.

Both are perfectly valid.

The former is more prevalent in the US, the latter in international/GB Enlgish.

Be consistent about which you use.

Also, the pronoun I is always capitalized.

Peter correctly says that omitting the serial comma is common in the US. That does not mean that it is considered correct in the US.

All US style manuals encourage the use of the serial comma -- and as I am fond of repeating, forgetting the comma can have serious legal implications. If I write: You will do action A, action B and action C -- how many actions have I told you to do? 

In the context of construction contracts and specifications, the courts have repeatedly held that, without the serial comma, I have asked you to do TWO items, not three. This error has cost owners tens of millions of dollars.