There's an article well worth your time at The Phoenix by David S. Bernstein called "It Wasn't a Dream: Four signs that the Democratic gains in 2006 could mark the start of a new, blue era in American politics."
While it's written for a Boston audience, and it comes from a liberal perspective, the piece is cogent, well argued and not easily dismissed. Plus, if you're a liberal, your heart will beat faster and it will be very hard to keep a smile off your face.
Bernstein's argument is divided into four parts:
1) Congressional-numbers game
2) Statehouse control
3) There aren't enough married middle-aged white men
4) This is the modern world
The piece is spread out over three pages and the point here is to recommend the article, not to summarize it. However, here is one snippet that will give you a feel for where Bernstein is coming from...
If anything, the Democrats’ slim 51-49 edge in the Senate figures to expand significantly in 2008, when the Democrats will have to defend just 12 of the seats they now hold, while 21 Republican seats will be in play. Some neutral observers are already predicting a four-seat gain for the Democrats in ’08 — and at least one Democratic pundit comes in at nine.