The following NYTimes website provides a succinct side-by-side comparison of the House passed bill and the Senate Bill proposed by Majority Leader Sen Harry Reid. There are only a few differences, but some, like the lack of an employer mandate in the Senate bill, are significant.
http://www.nytimes.com/interactive/2009/11/19/us/politics/1119-plan-comparison.html?h#tab=0
The Kaiser Family Foundation has a tool that allows you to compare features of the House passed bill to single payer bills in the House (Conyers bill) and Senate (Sanders bill). The tool will be updated to include the Senate/Reid bill shortly.