I predict the Dems will pick up 2-3 seats in the Senate and 8-10 in the House. Not enough to take the majority, but enough to cause more problems for the lame duck Bush Administration, and to set them up for a possible majority in 2008. This is basically what Charles Cook has been predicting at www.Cookpolitical.com for the past few months, and it doesn't appear that anything fundamental is changing to alter things. The GOP has been a strong finisher in recent elections, and though the Dems have a strong edge now, it is doubtful that they can translate this into taking over either house of congress in 2006.
Paradoxically, as things continue to go poorly over the next two years, this may set the stage for a dramatic shift in the political landscape in 2008, decreasing the chances that McCain or Giuliani will end up with a Republican dynasty in the White House and an ongoing dominance of the Congress.