One of the people I follow on twitter sometimes ends his sentences in ぞと. Is this just a more polite form of ぞ？
Here's an example:
So your example roughly means, "There, I've posted a new blog article." And no, it doesn't add any politeness to the sentence.
The preceding sentence is usually in volitional form, like
Note: depending on the context, there are cases that ぞと should be parsed as 「...ぞ」と, as explained in istrasci's answer.
The only thing I can think of (without any context provided) is that this would be used when quoting what someone else said. Like:
I would split the example sentence into two parts:
Unfortunately, I cannot explain how the と affects the other part well, but as far as I can say as a Japanese, the と is a kind of like an interjection and its effect is vanishingly small, at least not making the sentence more polite.
FYI, Reno, a Final Fantasy 7 character, often ends his words with