Rhenquist will probably not be able to keep his duties for much longer. From the current court, I think Ruth Bader Ginsberg is probably the most qualified to be the next Chief Justice. Sandra Day O’Connor would be an interesting choice. However, age would probably disqualify her.
Any other suggestions from doper-land?
Justice Scalia
I thought it went to the justice with the most seniority…
You are truly scary.
The President can nominate anyone to be Chief Justice. It almost never goes to the judge with the most seniority.
Justice Thomas, then?
Justice O’Conner is a sensible moderate, and a woman to boot. She’d be good.
How often is a sitting Justice made Chief when the current Chief retires?
I don’t recall it happening.
I agree, she did have the common sense that God gave a goose to “vote” for President Bush! 
It happened with the current one. Rehnquist was promoted from Justice to Chief Justice back in 1986
Another strike against Ronald W. Reagan!
I also found:
Harlan Stone, Earl Warren, and Eward White.
It isn’t a common practice but it certainly isn’t all that rare.
Earl Warren was governor of California before becoming Chief Justice on a recess appointment. He was later confirmed by the Senate.
Warren had never been a judge before becoming Chief Justice.
Any sitting member of the court who was named Chief would be filibustered. Unless Bush wanted to start the mother of all political battles, Scalia and Thomas will be Associates until they die or leave the court.
Robert Bork 
Bork, though an excellent choice, wouldn’t fly for many obvious reasons.
For one thing, he’s probably too old as well.
An aside, I hear rumors Scalia is considering leaving the court because he’s realizing his ‘conservative’ views of the law’s role and government are never going to command a majority.
Scalia often votes in the majority, so I’d just assign this to idle bs, myself.
If Scalia writes in a 9-0 decision to make Cheney open up the books about energy policy, after all teh turmoil, then he is a shoo-in.
If the Court opens up on Bush’s watch, Bush has every reason to nominate Scalia – he’d be very pleasing to social conservatives, an easy sop to their feelings while not directly offending the fiscal conservatives.
The Chief Justiceship is more of an honorary title than anything else – he controls some of the court’s administrative functions, and ostensibly assigns authorship for opinion-writing when he is part of the majority, but there’s no significant real additional power to the position that an ordinary Justice does not already possess.
Given history, it’s likely that if Rhenquist steps down, an entirely new person will be appointed Chief.
The only candidate on the current court I see is Scalia, and that only as a way to honor his long service on the bench (and his ideological closeness to Bush), which is much the same reason Reagan gave the title to Rhenquist. But even that is unlikely to happen; Bush critics, having already demonized Scalia to the nth degree, would seize on such a move as “further radicalizing the court” (even though it would not actually change the balance of power in any way), and really, Bush doesn’t need that kind of a hassle. Political expediency will make it far easier to just find a new person.
Gotta admit I’ve always found that weird. Just appointing a chief justice from outside the current group. I always thought it would make more sense to let the justices pick the chief justice and allow the president to nominate the associate judges when opening occur.