Unforgivable?

Is there an unforgivable sin in Islam? Most would refer to shirk as being the one unforgivable sin in Islam.

S 4:48 Allah does not forgive that he be associated with but forgives what is other than that, whom he wills. And he who associates with Allah has fabricated a great sin.

S 4:116 Allah does not forgive being associated with but forgives what is other than that, whom he wills. And he who associates with Allah has strayed far.

Regarding the question of forgivability, see:

Does Allah forgive shirk?

Quran Contradiction: Does Allah Forgive All Sins Or Not?

However:

S 3:90 Those who have disbelieved after their faith, then they have increased in kufr. Their repentance will not be accepted and those, they are the straying.

S 4:137 Those who have believed then disbelieved then believed then disbelieved then increased in kufr--Allah would not forgive them nor guide them on a way.

We might add S 4:17 Repentance is only on Allah for those who do evil in ignorance then repent soon afterwards.

Does Allah forgive one who commits sin knowingly?