Can you imagine the "Expecto Patronum" of Voldemort???

Not a bad speculation...I don't know what his patronus would be like. I have my doubts that Voldemort could even cast it due to the fact I don't believe he has a happy memory left in him. Unless you count killing thousands of people and enslaving them. Maybe those are the happy thoughts of mass murders. I wouldn't know...I'm not a murderer!

I can also only imagine a snake coming out of his wand for this spell. Because I can not think of a more poisonous creature than snake. But I have my doubts weather he will need this spell or not. This spell is bascally used to keep dementors away. I do not think dementors can be dangerous to him. He can be dangerous for them.

I'd imagine Voldemort's Patronus to be a snake of some sort. Normally the patronus reflects something about the person who cast it, for example Harry's is a stag, the animal his father could transform into. And Voldemort is always characterized as a serpent, and his "loyal pet", Nagini, is a snake. I think it;s the only one that makes sense.

I agree that the spell needs a happy memory for it to be cast. I don't think Voldemort has any bit of happiness in him. But, more importantly is the fact that Voldemort wouldn't need to use it as the dementors are at the very least his allies if not completely under his control. So, he might never had a need to cast this spell.

What everyone seems to be forgetting is that happiness is a relative term. Happiness is something that makes you, personally, happy, not something that is good. For someone sadistic and twisted like Voldemort, a memory of his youthful days when he would trick people into doing what he wants or torturing a particular victim might make him happy, so he could in theory cast a Patronus. However, what you all seem to be missing is the most crucial factor: the Dementors, who are the sole purpose for the Patronus, are Voldemort's slaves and therefore do whatever he wants, so why would he need to repel them? As for what it would be, I doubt it would be a snake, though it's possible; however, a Patronus is a shield against harm, something behind which nothing can reach you. For Harry, it's a Stag, which is what his father could transform into when he was alive; this symbolizes that Harry finds protection and love at his father's memory. In Voldemort's case, he believes that he is the strongest wizard in the world and the ultimate power, so it's my conclusion that IF Voldemort had a Patronus, it would, in fact, be himself.