Via Hot Air Headlines, the last poll from American Research Group, Inc. before the actual vote in tomorrow's special election has come out, showing Brown ahead of Coakley 52-45, with Kennedy tied with "undecided" at 2% each. The poll of was conducted from January 15-17 and consisted of 600 randomly selected likely voters, of whom 42% were Democrats, 15% were Republicans and 43% were not enrolled with either party. The margin of error is +/-4%. That means that Brown's lead as reported by this poll is within the margin of error.
I think that news is actually a little more striking than it appears, since 51%, not 43% of Massachusetts voters are independent, with only 13% Republican and 36% Democrat.
If you take the internal percentages of each group reported by American Research and then weight them for party affiliation, the split becomes Brown 53.5%, Coakley 43.8%, Kennedy 1.7% and undecided 2%. Brown's lead goes from 7% to 9.7%, beyond the margin of error.
Of course, weighting the sample like that assumes that the percentage of actual voters who turn out tomorrow will be divided 51/36/13, Independent, Democrat and Republican.