U.S. House elections
Prior to the 2008 elections, the Democrats held 236 seats in the U.S. House, to 199 for the Republicans. After the elections, they held 257 seats, to 178 for the Republicans, a shift of over 20 seats. Considering that the Democrats had made substantial gains in the 2006 elections to become the majority party in the House, the 2008 results were a remarkable victory.
U.S. Senate elections
Prior to the 2008 elections, the Democrats held 51 seats in the U.S. Senate, counting two independents who caucused with the Democrats. After the elections, they held 59 seats (again counting the two independents who caucus with the Democrats), to 41 for the Republicans, a shift of 8 seats, also a remarkable gain.
Information on individual House and Senate races is available at: http://www.cnn.com/ELECTION/2008/