There's a number of different routes that he could choose.
I think one major option is Governor Richardson. I think Richardson decided to endorse Obama because he thought that he would be more useful to him than to Sen. Clinton and that he therefore had a better shot of getting on the ticket. He makes up for a lot of Obama's weaknesses, he does have years of very diverse experience, Governor, Congressman, UN Ambassador, Energy Secretary. Already, he has executive experience and foreign policy credentials, two areas where Sen. Obama is considered weak. He would also, as a Hispanic, theoretically bring in large shares of the Hispanic vote, where Sen. Obama has been losing to Sen. Clinton throughout the primaries. I think if Obama picks Richardson it is a signal that he is going after the West in the general election even though his opponent is an Arizonan with appeal among many Hispanics (because of the immigration bill). Obama's losses in Ohio, Pennsylvania, New Jersey, West Virginia, and likely Kentucky show a real weakness in the Rust Belt. If he's at risk of losing these states to Sen. McCain he has to make it up somewhere. He can start in the West, Richardson's New Mexico, Colorado, Nevada. The West has been talked up by a lot of people as the future battleground and the North and Southeast solidify in blue and red, respectively.
Another option, go with a Virginian. Sen. Obama won big in Virginia, its been talked up as a swing state, with the growth of Democratic Northern Virginia. 13 electoral votes and it could be a crucial state. Three real options here, Gov. Kaine, former Gov. Warner, and Sen. Webb. Kaine was an early supporter of Obama, the first Governor in the nation to endorse him in the primaries. He's very popular, but also has little experience, which is why I think Obama will not go with him ultimately. Former Gov. Warner is incredibly popular in Virginia, talked about as a possible 2008 Presidential candidate himself, but opted out and decided to run for Senate, which is why I don't think they'll let him go on the ticket this year, as Warner almost guarantees a Senate seat pickup for the Democrats.
Probably the Virginia Democrat that gets the most buzz is Sen. Jim Webb. Webb was elected in 2006, defeating Sen. George Allen, considered at the time to be a top contender for the GOP nomination for the Presidency. A true "giant killer" Webb is a former Republican, President Reagan's Secretary of the Navy, who switched to the Democrats over his opposition to the Iraq War, and has a son in Iraq. A compelling story, an appeal to these white blue collar voters whom Sen. Obama has had a hard time with lately, military experience, foreign policy credentials. On paper, a great pick. I think there is one roadblock, however. Given that Sen. Obama will have to work hard to regain women voters who voted for Sen. Clinton in the primaries, and I think Webb could hurt him on that front. Mainly because there is some controversey with him. Webb is on his third wife now, who is significantly younger than him, there has been some controversey about his writings as well, particularly, here's the kicker, an article called "Women Can't Fight" Webb's argument against women in the military. This got some play when he was running for Senate, but keep in mind, local media vs. national media, big difference, the national media will pick up on this, big time, and Obama needs to keep that in consideration as he ponders Sen. Webb on the ticket.
Keeping women in mind, there are a number of different choices for women VP candidates that Sen. Obama could explore. Sen. Blanche Lincoln of Arkansas, a moderate Democrat, a Clinton supporter. Gov. Kathleen Sebelius of Kansas, I don't think a Democrat picks up Kansas with or without her, the hope would be that her appeal would be broader. I think Gov. Napolitano of Arizona would have a better chance if the Republican standard bearer weren't also from Arizona, although McCain's numbers have been surprisingly weak in his home state.
To be honest with you, given the political climate, the Democrat should be the frontrunner, and they are, but I remain very skeptical and very curious as to how Sen. Obama gets to 270. I can see a clear, traditional route for Sen. Clinton, Kerry's states plus Ohio, plus West Virginia, plus Arkansas, I'm not sure what Obama has up his sleeve, he's attracted a lot of new and diverse voters for him, but I remain unconvinced how and if this translates into state victories, he has to remember, that he won this primary because of proportional representation, had Clinton won all the delegates in California, New Jersey, New York, Ohio, Pennsylvania, etc, it would have been over a long time ago. Obama's team really worked this system very cleverly and effectively to come out on top, but when you get to the general election, its winner takes all, you win a state by 1 vote the winner gets all and the loser gets none.