Mark Blumenthal projects a 48 seat gain for Republicans in the House. On the Senate:

The 86% probability we are reporting (as of this hour) on the Election Dashboard of Democrats maintaining their majority [in the Senate] assumes that each state's result is statistically independent. However, if the polling has a national bias – a subject discussed here in more detail this morning -- the chances of a single party sweep of the close races is likely much greater. So while Democrats are likely to retain control, the potential for a Republican Senate majority remains very real.