Joe Biden, though he won re-election (like the other guy named Joe who ran as the Vice President and concurrently ran for re-election), will become Vice President next year, opening up the Foreign Relations Committee chair.
Robert Byrd has now entered the "Strom Thurmond" mode of his Senate career, though to be crude, Democrats don't care nearly as much about his health as Republicans cared about Strom Thurmond's, because
a) Democrats have a more significant majority than the Republicans (in 2000 it was 50-50 until Jeffords left the party)
b) West Virginia re-elected Democratic Governor Joe Manchin, so if Byrd dies, he'll be replaced by another Democrat; had Thurmond kicked it between 1999 and 2003, Jim Hodges would've appointed a Democrat to replace him.
Anyway, befitting that mode's status, Byrd will no longer be chairing the Senate Appropriations Committee.
That goes to Dan Inouye of Hawaii, octogenarian war hero and more recently, defender of Republican convicted felon Ted Stevens.
As Inouye chaired the Committee on Commerce, Science and Transportation during the 110th Congress, that seat becomes open; it's unclear whether Inouye, Rockefeller, or a future chair was/will be the first chairman of the committee in charge of regulating the Internet who knows how to use it (since John McCain and Ted Stevens clearly could not, and I doubt Fritz Hollings could in 01-02; unless Pressler could in 1995-1996 (unlikely) that means there was never one at least until this Congress).
Rockefeller is currently Chairman of the Select Committee on Intelligence, which would then apparently go to Senator Dianne Feinstein of California, who currently chairs the Rules Committee.
That committee is likely to be chaired by Chuck Schumer, the highest-ranking Democrat on the Committee neither in Strom Thurmond mode or chairing a different Committee.
The chairman replacing Joe Biden on Foreign Relations is not as clear.
Should Barack Obama appoint Senator Kerry to be Secretary of State (there are rumors that he's angling for it but it is by no means a sure thing), it would go to quite liberal Senator Russell Feingold of Wisconsin.
Otherwise, it would go to Kerry, who currently chairs the Small Business Committee; most senior member not currently chairing a Committee (and nobody's going to want to switch to Small Business chair) is Mary Landrieu of Louisiana.
If Lieberman is kicked out of his committee chairmanship, it's also unclear. If Daniel Akaka of Hawaii wants to switch from being chair of Veteran's Affairs, it would go to him, and he'd be replaced on Veterans Affairs by Patty Murray of Washington.
Otherwise, it would go to Tom Carper of Delaware.