I have just updated my chart of all U.S. Senate seat holders from 1978-present (organized by state, color-coded by party) to reflect the 2004 elections. I have also highlighted (with red asterisks) the seats up in '06.
http://www.hs.ttu.edu/research/reifman/senatedata.htm
At the bottom of the chart, I list the party breakdown for each two-year session, as well as the number of states having both of its U.S. senators from the same party (which has been going up over time). I believe that increasing numbers of states with both senators from the same party reflects increasing polarization. Sure, some examples are spurious (e.g., North Dakota has two Democratic senators even though it's a "red" state at the presidential level). On the other hand, states such as GA and SC now having two R senators and DE, MI, and IL having two D senators represents movement in recent election cycles consistent with presidential voting patterns.