Can someone give me some important quotes in Othello regarding Iago and his "honesty"?

You are quite right to put "honesty" in quotation marks,
for any mention of Iago as being honest must be ironic.   However, the irony is mostly
dramatic.  All of the major characters believe that Iago is honest, so when the term is
used, the audience knows that each of these characters has misjudged
Iago.

One of the first references to honesty is made by
Iago himself, in the last few lines of Act 1.  He characterizes Othello as one
who

is of a
free and open nature

That thinks men honest that but seem
to be so

A perceptive judge
of human nature, Iago understands that Othello is truly honest, and because he is so, he
sees others as he is himself.  Thus, Iago knows that Othello will trust
him.

Later, Cassio calls Iago "honest" after Iago gives
Cassio advice that will result in Othello's ordering Cassio's
death:

Good night, honest
Iago.

But the term reaches
its highest irony when Othello calls Iago honest:

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And, for I know thou'rt full of love and
honesty

And weigh'st thy words before thou giv'st them
breath.

And later, Othello
declares,

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This fellow's of exceeding
honesty,

And knows all qualities, with a learned
spirit

Of human dealings. (Act 3, scene
3)

These references to Iago's
honesty, while initially are somewhat humorous because the audience knows how grossly
Othello has misjudged Iago and his intentions, are the key to understanding why Othello
falls for Iago's machinations and turns against his most beloved wife Desdemona.  It is
Othello's faith in those around him, his tendency to see others as he himself is, his
trust in the men who have served with him in battle that leads to Othello's downfall.
 In other words, much of what causes Othello to turn against Desdemona is his inability
to see the darker nature of Iago.