Illinois Treasurer Alexi Giannoulias plans to seek the Democratic nomination. His friendship with Obama may help, but the White House had been recruiting Madigan to run.

Christopher Kennedy, who runs Chicago's Merchandise Mart, is another potential candidate.

Cheryle Jackson, president of the Chicago Urban League and former Blagojevich spokeswoman, is exploring a bid. Jackson, who is black, could benefit from any pressure to keep a black senator in the seat.

Illinois state Rep. Arthur Turner said while some of that pressure will exist, race won't be an absolute requirement.

"They're not going to throw down the gauntlet if a black is not slated for that position," said Turner, a black representative from Chicago.

On the Republican side, Rep. Mark Kirk is considering running, as is Andrew McKenna, chairman of the Illinois GOP.

Speculation about Kirk's intentions in particular have run rampant for weeks, but spokesman Eric Elk said Friday that there was no timeline for an announcement from the representative in his fifth term serving Illinois' 10th district in Chicago's northern suburbs.

Burris' decision to bow out caps a long political career that included stints as Illinois' comptroller and attorney general.

Blagojevich appointed Burris in December, just weeks after the then-governor was arrested on charges of trying to sell the seat.

Burris has maintained he did nothing improper to get his Senate appointment, but it triggered waves of criticism, opposition from fellow Democrats, court battles and even a perjury investigation, which did not produce any charges. Democratic leaders initially vowed not to seat him, but eventually relented. Burris still faces a Senate ethics probe.

He never received backing from top Illinois politicians, including fellow Democratic Sen. Dick Durbin, who has said repeatedly he would not support Burris for a full term.

Burris seemed to acknowledge the travails of the last seven months in his announcement.

"Serving in public life is not easy, " he said, "but it is a noble and rewarding calling."