In chapter one, Snape tells Voldemort that he is certain about which night Harry is being taken to the Burrow, because of the contact that he and Voldemort talked about. Later we find out that Snape's contact is Dumbledore's portrait. But who does Snape tell Voldemort that the contact is?

i don't think snape ever said...he just said contacts at the ministry...voldemort probably could care less who told him as long as he knew...doesn't strike me as one to care about details very much.

No, I thought Yaxley said he got it from the Ministry, not Snape. Snape never said, but this is HARRY POTTER. This one battle could take out ALL of Voldey's opposition for good. I'm sure he'd care, especially is Snape, his main man, talked to him personally about it.

i think he was talking about mundungous but i am not sure or it was dumbledore's portrait

I think Snape said Mundungus, bbut it was Dumbledore's portrait. Somethin like that.

I don't really remember. I think it was either Mundungus or someone from the Ministry...but I'm not one hundred percent sure. That's an interesting question!

I'm pretty sure it was Mundungus that Snape was talking about... Much much later, in 'The Princes Tale', we see Snape discussing it with Dumbledore's portrait, and they say about how Mundungus said it would be that date of Harry's moving, and that Snape is to instruct Mundungus to have an idea about using polyjuice potion to confuse the Death Eaters...

it's definetly a confunded Mungunus Fletcher ...you can figure that out of Snapes memories where he talks to DD and indeed says that...he adds that he didnt give away all of the plan (7 Potters) but only the date so that LVs trust in Snape is even more strengthened...and it was DDs potraits idea to do so...

Plus, in The Prince's Tale, they show Snape imperio-ing Dung. Didn't they? I'm pretty sure they did....

No, he confunds him, he doesn't imperius him. And, yes, it was mundungus, though I don't think Snape would have told Voldemort that he confunded him, he probably told Voldy that he tricked him into releasing the date and method, or used legilimency, because dung is not exactly portrayed as a genius, so it would have been easy for voldy to believe that snape weezled info out of him.

it was mundungus wasnt it?
wasnt he under the imperius curse by snape
im sure it was something like that
but dont we find out it was dumbledores plan for him to get the right night otherwise hed suspect snape?
part of the whole plan thing?

maybe he tells him the truth after al he couldnt lie to voldemort or he could be in big trouble so maybe he just told him that dumbledor told him.

Well...After completing the book this question was still left lingering in my mind. In the Prince's Tale it did show Snape and Dumbledore talking about a confunded Mundungus and how he'll make the order agree on the seven potters idea. In the first chapter it was not told who the source is- ministry was used as a source by Yaxley. Snape just said,'the source we discussed earlier'.
If it was Mundungus he was referring to then how is it that voldemort took Mundungus seriously when most of the wizards think of him as a crook and a snide person? Voldemort was suppossed to be the kind who trusted things which had iron clad proofs. That is the reason he trusted Snape and not Yaxley. BUt how could the source Snape referred to be Mundungus as all of us are discussing???

I need an answer for this question people. Please do answer this if anyone of you has a convincing one.