The democrats appear poised to pick up at least 5 Senate seats currently held by the republicans without losing any. There are also 2 tossups currently held by republicans, Wicker in Mississippi and Dole in North Carolina.
FiveThirtyEight.com, CQ Politics and Electoral Vote all have recent analysis of polls and predictions.
FiveThirtyEight.com (as of 10/4)
Electoral-Vote.com (as of 10/4)
Current Senate Map from CQ Politics
Latest Senate Polls: