Libraries for Online Machine Learning I am looking for packages (either in python, R, or a standalone package) to perform online learning to predict stock data.

I have found and read about Vowpal Wabbit (https://github.com/JohnLangford/vowpal_wabbit/wiki),
which seems to be quite promising but I am wondering if there are any other packages out there.

Thanks in advance.
You could look at scikit-learn or Orange module in Python.
Scikit-learn has a SGD classifier and regressor that could do a partial fit data in case of online learning.
In R, take a look at caret package