Today (yesterday)

Bush 50 (50)
Kerry 47 (46)

The Washington Post tracking poll will be conducted daily until election day. Results are based on telephone interviews with a randomly selected national sample of adults, including self-identified registered voters and likely voters.

[...]

This tracking poll is based on a rolling three-day sample. About 350 likely voters are polled each day. To update the numbers, a new day's sample of respondents is added to the total sample and the oldest day's sample of respondents is dropped out. The Post typically identifies likely voters as those who say 1) they are registered to vote, 2) they are absolutely certain to vote, and 3) either voted in the 2000 election; or are between 18-21 years old and are closely following the race. This typically produces a sample that is between 55% and 60% of the voting age population.

10/18: 1,656 likely voters; 2,130 self-identified registered voters Oct. 14-17.

10/17: 1,648 likely voters; 2,115 self-identified registered voters Oct. 13-16.

Link.

I don't particularly trust their likely voter model as there are so many newly registered voters that will not be picked up by the poll, but I think the Post is generally right in that the race is within the margin of error at this juncture, and anyone who tells you they know who is going to win based on current polling doesn't know anything.