The Nats acquired Josh Willingham (and a crappy pitcher) for Emilio Bonifacio and two prospects, leaving them with Elijah Dukes, Lastings Milledge, Willie Harris, Austin Kearns, and Wily Mo Pena on the outs. Even if Willingham is shifted to first to replace annual paraplegic Nick Johnson the Nats are still looking at a bit of a log jam. Kearns makes the most of the potential benched players (8 mil in 2009, then 10 mil club option) which would probably be eaten by the Nats in exchange for a slightly better return. That or Kearns could be waived and (or) released, which would leave the Rays paying less than 400k (assuming the Nats would try to sneak him through on irrevocable outright waivers and send him to the minors. Not a guarantee) for his services in 2008 and able to decline his option (1 mil buyout) in 2010.
Why would the Rays want Kearns? Well Sean Smith has Kearns worth 7 runs in a corner outfield position, so nearly a win. Plus Kearns' wOBA* the past three years are, as follows in recent-to-past order: .302, .352, .372. That's from a right-handed hitter in his prime with plus defense. To give you an idea of where that puts Kearns amongst outfielders, Matt Kemp's wOBA* this season was .353, and that's without the sexy defense.
If the Nats decide to move Harris (14 runs in the corners) the Rays should probably at least inquire. Over his last ~800 PAs he's shown the ability to be a .350 wOBA* player, and that's with some unlucky ball in play data last season. Mo Pena? I'd rather not see him as an outfielder, and I'm unsure his bat plays well as a part-time DH.