Rasmussen Reports issued these poll results on May 18. One of the questions listed 4 candidates: Obama 42%, McCain 38%, Barr 6%, Nader 4%, undecided 11%.
Another question listed 5 candidates, with Hillary Clinton running as an independent: McCain 32%, Obama 31%, Clinton 22%, Barr 3%, Nader 3%, undecided 9%.
Another question asked whether the respondent felt about the chances that someone other than the Republican or Democratic nominee would be elected president in the next 25 years. 10% said this is Very Likely; 29% said Somewhat Likely; 52% said Not Likely; 9% said undecided.