Chico Harlan of the Washington Post is reporting the Rockies acquired left handed pitcher Joe Beimel from the Nationals to bolster their bullpen, although it's unclear at this point what they've sent in return.
Earlier reports linking the Rockies to Beimel indicated that they were asking for Eric Young Jr., but the Rockies were reluctant to part with their second base prospect. As more comes out about this trade, we will update.
UPDATE: MLBlogs is reporting that the trade is "for two minor league pitchers" but not Eric Young.
UPDATE II: Troy E. Renck indicates that Sky Sox closer Ryan Mattheus might be one of the pitchers returning to Washington. Beimel's agent says he's excited about the opportunity to play with the Rockies.
UPDATE III: Per the comments, MLB Network reported the trade is Beimel for Mattheus and 23 year old RHP Robinson Fabian. The Nationals get a couple of live arms, but there's plenty of risk from their end.