There were two U.S. Senate races that were too close to call.
These matter more than the several close U.S. House races (where a Democratic majority is clear and there are no filibusters), and the President race where Missouri remains close, but the electoral college victor is clear so it doesn't matter. In contrast, each additional U.S. Senate win for the Democrats reduced the viability of Republican filibuster threats. It takes 60 votes to overcome a filibuster, but moderates in each party often differ with fellow party members on filibuster voters, so each vote matters.
An analysis from last Friday of the votes remaining to be counted in Alaska suggests that Democrat Mark Begich who is currently trailing in the count, is likely to prevail over incumbent Republican U.S. Senator and convicted felon Ted Stevens. New information about the number of votes still uncounted in that race improve the Democrat's chance.
Minnesota Democrat Al Franken is also closing the gap with incumbent Republican Norm Coleman in the U.S. Senate race in Minnesota which is likely to produce a recount after the first round of voting is over. At last count, 206 votes out of 2.88 mllion cast separated the candidates (with Coleman's early lead eroding).
There will be a runoff election in Georgia, but it would be very hard for the Democrat in that race to prevail. The Republican won 49.9% in the first round, and about 3% went to a Libetarian candidate who is not in the runoff. The Democrat will need to win essentially 100% of the Libertarian vote to prevail, or will have to win over a lot of people who voted for the Republican the first time, and will have to maintain excellent voter turnout. The runoff is in early December.