This is an interesting discussion because it reveals just how little insight certain Republicans have into the thinking of the Democratic presidential candidates. It is the informed conventional wisdom of those who cover the campaigns that neither Clinton nor Obama will be seeking additional demographic diversity on their tickets, and instead will both most likely look for a white man from a swing state who can bring its electoral votes to the table with him. Hence, Dianne Feinstein would seem a highly unlikely pick for Obama. Safire's prediction that Clinton might choose Rahm Emanuel, while intriguing, would also seem unlikely, though in choosing him Clinton would gain a real brawler of a campaign partner -- something that's an absolute must for her.
Also, my understanding is that Wesley Clark would be an unlikely choice for Clinton, even though he's got the right sort of demographic background -- white, Southern, military, and from the potentially swingable (for a Clinton) state of Arkansas. His performance in 2004 has raised concerns about his skills and abilities as a campaigner that would need to be assuaged.
The names that come up most frequently in discussions of a possible Obama V.P. pick are Jim Webb and Mark Warner, two centrist Virginia Democrats from the one Southern state that's previously elected an African-American to the governor's mansion. Webb also has a military background. Marc Ambinder reported on the Obama-Warner possibility in June, and The Washington Post's report from yesterday morning on Webb's efforts to stand up to Clinton within the Senate provide intriguing hints of what may be efforts on Webb's part to prove himself a worthy partner for Obama. On the other hand, Webb has also co-sponsored legislation with Clinton, so he's hardly foreclosing his options.
As for Gen. David Petraeus, I'd be surprised if he tossed his hat into the ring before 2012, should he ultimately decide to do so.
UPDATE: A commenter says that Democratic Ohio Gov. Ted Strickland is on Clinton's short list, as well. I don't know who the commenter is so can't assess the veracity of that claim, but he sure sounds like a good idea and, though he lacks the military connection, he'd otherwise fit the Clinton bill to a T.
--Garance Franke-Ruta