The Economist has picked up on Daley's departure:
After Mr Daley privatised the city’s parking meters, drivers filled coin slots with glue and docile aldermen briefly located their spines. Last year Mr Daley struggled to close a budget gap. This summer just 31% of Chicagoans thought he should seek re-election.
So who will succeed Mr Daley? The most promising contender may be Mr Emanuel. Whoever the replacement, he is unlikely to bring the dramatic changes that characterised the Daley era. But a new leader is overdue. “Simply put,” Mr Daley said, “it’s time.”
And the Guardian:
Speculation in Chicago and Washington DC quickly turned to [President Obama's chief of staff Rahm] Emanuel, who has long made public his interest in the job – while the timing could not be better from the White House's point of view. With a crushing defeat in the US midterm elections looming, the need for Obama to reshuffle his senior staff after November was growing.
Emanuel refused to comment on the speculation, saying in a statement: "While Mayor Daley surprised me today with his decision to not run for re-election, I have never been surprised by his leadership, dedication and tireless work on behalf of the city and the people of Chicago."
Note that Emanuel was my Congressman until being named Obama's chief of staff in November 2008, and he maintains a permanent residence in the city.