This is the second time I have typed this out...I accidentally hit who knows what on the keyboard, and lost my first analysis. Since I was working on the GOP at the time, I'll start with the dark horse for the McCain ticket.
Admitedly, I struggled to come up with a "dark horse" for VP for McCain. I think that whomever McCain picks should be youthful and photogenic. McCain is the one with the record. McMorris-Rodgers rose quickly through the GOP ranks as a State Rep., and became the youngest (and first female) house Republican leader in state history. As a congresswoman, she has focused on veterans' and environmental issues. She has also become an advocate for women's issues. She helps in several areas, providing a balance to McCain's age, but also has her own merits as the VP choice. Not a household name, but what dark horse is? I'm not aware of any major issues/scandals that would render her disqualified, perhaps one of our Washington posters could help out! 
For the Democrats...
Caperton, Governor of West Virginia from 1989-1997, lends considerable experience to the ticket. He defeated an incumbent Republican Governor in his first run for office (granted, the incumbent was Arch Moore, who had long been allegedly corrupt). As Governor he greatly improved the state's educational situation and raised teacher pay. He also improved the fragile economic conditions in West Virginia, lowering unemployment by nearly four percent and in the process creating 86,000 new jobs. He also aided West Virginian tourism, through the creation of Tamarack, a museum and art gallery. Since 1999, he has been President of the College Board and has been received great acclaim for his efforts. An education crusader with a strong record of economic improvement in a domestic policy oriented election deserves a look. There are two things which may cause issues, and I will try to refute these. First of all, Caperton is 68. Mr. Morden and I have discussed the importance of age in the Veepstakes, and I do concede that the age may be a factor. However, Joe Biden is 66 and probably being seriously considered. Caperton should also be given some consideration. Also, he is twice-divorced. This might not play well with value voters. I just wonder how much of an issue Obama's opponents would make of it. All in all, Caperton is a solid pick with a good record. I doubt such a pick would put WV in play, but it would go a long way toward assuaging the concerns of voters who think the ticket is inexperienced.
(Note: I think Mabus would be a good dark-horse pick as well)
McMorris Rodgers actually would be a good pick for McCain as a darkhorse VP. She is pregnant in that picture, and had the baby a little over a year, who was unfortunatley born with Downs Syndrome. She is truly pro-life and is married to a military man. As earlier stated she was the youngest and first female Republican leader in the Washington state house. She is conservative (member of the RSC) but not too conservative to scare off independents
Here's a more recent unpregnant pic
