I'll tell you

don't tell me

Used to introduce a guess at a fact or situation, as if forestalling the other speaker's utterance.

I can tell you

Emphasises the truth of a statement.

I tell a lie

I am mistaken; I thought that what I said (or wrote) was true, but I have just realised that it is not.

I tell you

Synonym of I can tell you.

I'll be

Expressing surprise.

I'll be a monkey's uncle

Often preceded by well: expressing complete surprise or disbelief.

I'll be bound

An expression of surprise.

I'll be damned

An expression of surprise.