I'd like to talk about Harkin and Daschle as VP possibilities. I've mentioned Daschle before, but I haven't heard much of a response, so I'll make the case for both Senators here, and you can rebut as you will.
Harkin has won four terms to the US Senate from Iowa. He is experienced in national campaigning, having run for President in 1992, and is famously combative on the campaign trail. He served in Vietnam ferrying planes (I don't know if he actually saw combat), and growing up in a working-class immigrant family, has a deep understanding of the populist politics which are successful in the swing states of the upper Midwest like Iowa, Minnesota, Wisconsin, and Missouri to an extent. He is the ranking Democrat on the Agriculture committee, which he chaired during the brief Democratic interregnum in the Senate from 2001-2002. He was also the keynote speaker at the memorial service for Paul Wellstone, and since Wellstone's death, he seems to have been positioning himself to inherit the mantle of fiery populist champion in the Senate. I think this is as close as we can come to a DC insider on the ticket with Dean who wouldn't obviously contradict many of the key parts of the Dean campaign.
Daschle has many similar advantages to Harkin. He also comes from a Midwestern working class background. He served as an Air Force Intelligence Captain during Vietnam, and clearly understands how to win in culturally conservative red states. He also would bring to the ticket all the legislative experience Dean could possibly ask for (10 years as his party's leader in the Senate), and while he did support the war, he was far more reluctant and eager to limit Bush than was, say, Gephardt. Daschle also brings two minor advantages -- he's a couple inches shorter than Dean, minimizing the effect of Dean's small stature, and Dean-Daschle is nicely alliterative.