What reasons does Iago provide for hating Othello?

At the end of Act II, Scene 1, Iago provides a few reasons why he despizes Othello so much. First, Iago acknowledges that, even though he cannot stand Otehllo, Iago knows Othello is

of a constant, loving, noble nature,And I dare think he'll prove to DesdemonaA most dear husband.

This, of course, gives him all the more reason to hate Othello, as he has qualities Iago obviously does not possess. Furthermore, the fact...

At the end of Act II, Scene 1, Iago provides a few reasons why he despizes Othello so much. First, Iago acknowledges that, even though he cannot stand Otehllo, Iago knows Othello is

of a constant, loving, noble nature,
And I dare think he'll prove to Desdemona
A most dear husband.

This, of course, gives him all the more reason to hate Othello, as he has qualities Iago obviously does not possess. Furthermore, the fact that Othello deserves Desdemona's love because he has these attributes gives Iago more reason to dislike him so intensely for, as he says,

Now, I do love her too;

Not out of absolute lust, though peradventure
I stand accountant for as great a sin,
But partly led to diet my revenge.

Iago concedes that he also has feelings for Desdemona, but knows these sentiments are borne from his desire for revenge, not just his desire for her. Iago also says another reason for his hatred springs from his suspicion that Othello had an illicit liaison with his wife, Emilia.

For that I do suspect the lusty Moor
Hath leap'd into my seat; the thought whereof
Doth, like a poisonous mineral, gnaw my inwards.

For this reason, Iago is intent on getting even. He will punish Othello for humiliating him. He plans to do this through manipulation and deceit. If Iago fails, he wants at least to make Othello incredibly jealous. 

And nothing can or shall content my soul
Till I am even'd with him, wife for wife,
Or failing so, yet that I put the Moor
At least into a jealousy so strong
That judgment cannot cure.

Many commentators believe, however, that Iago's hatred is born from an innate evil. He relishes the thought of hurting others just for the sake of it. The fact that he gives reasons for his hatred is just an excuse for the fact that he is evil by nature. It is for this reason that Iago bears only contempt for the good in others, as the first excerpt most pertinently indicates.