In addition to the usual suspects:
USelectionatlas.org is a fantastic resource, and has a pretty good array of political forums as well.
The Hotline, published at nationaljournal.com, is by far the best daily political briefing in the country, has a very extensive poll archive, and a number of very good columns. It is a (very expensive!) subscription site, but if you are a student, you probably have access to it through your school.