Well, In general, things that give skill bonuses seem to be more likely to have exceptional versions, since they can be increased without being overpowering.
There are some things that just aren't crafted a lot, and so may have an exceptional version, even if they don't appear in the forums...
For instance, I only learned recently that cougar boots can be exceptional... just not many people make them.
As far as the lich claws... again, not many people make them, there's a very very narrow demand, and many crafters (like Drexia) would probably refuse to make something that has that kind of evil taint to it.
Hoods as well, I don't know of exceptional hoods, but given that they aren't made often, it's quite possible that there is an exceptional version, but no one has done it yet.
To make an exceptional item, you have to roll a 20 on the crafting roll, and then the game makes a confirmation roll with the same odds as you would normally have to succeed. (so if you have a 50% chance of making an item, you have a 2.5% chance on any given attempt to make an exceptional one)
The thing is, if you succeed in crafting something, the roll is hidden. So there's no way to prove that something -can't- be made exceptional.