No difference between the political parties?
The National Journal ranks politicians from most liberal to most conservative. The most liberal Senator is in the top most left square and the most conservative in the bottom most right square. In the Senate, as this picture above shows, there is virtually no overlap between the political parties in the Senate. Olympia Snowe is to the left of a couple Senate Democrats, but that is the only overlap. Snowe gets this relatively liberal ranking primarily because of her votes on social issues.
It is much harder to see the differences for the House because the pictures of individual members of the House are much smaller, but given the number of congressmen there is really not much more of an overlap. Michael Castle (R-DE) is the most liberal Republican and Bobby Bright (D-AL) is the most conservative Democrat, but both are fairly close to each other (both are on the 12 row within 16 spaces of each other).
The information on the 2009 vote rankings is available here.