The Collaborative International Dictionary of English v.0.48:

Logrolling \Log"roll`ing\, n.
   1. (Logging) The act or process of rolling logs from the
      place where they were felled to the stream which floats
      them to the sawmill or to market. In this labor
      neighboring camps of loggers combine to assist each other
      in turn. --Longfellow. [U.S.]
      [1913 Webster]

   2. Hence: A combining or mutual agreement in which one
      politician supports or assists another in consideration of
      receiving assistance in return; wheeling and dealing; --
      sometimes used of a disreputable mode of accomplishing
      political schemes or ends. [Cant, U.S.]
      [1913 Webster]

WordNet (r) 3.0 (2006):

logrolling
    n 1: act of exchanging favors for mutual gain; especially
         trading of influence or votes among legislators to gain
         passage of certain projects
    2: rotating a log rapidly in the water (as a competitive sport)
       [syn: birling, logrolling]

Moby Thesaurus II by Grady Ward, 1.0:

34 Moby Thesaurus words for "logrolling":
   backscratching, barter, cloture, committee consideration, debate,
   deliberation, division, even trade, filibuster, filibustering,
   filing, first reading, influence peddling, introduction, lobbying,
   lobbyism, political influence, pork barrel, public opinion,
   roll call, second reading, social pressure,
   special-interest pressure, steamroller methods, swap, swapping,
   switch, tabling, talkathon, third reading, trade, trading, vote,
   wire-pulling