Two important things are happening this year: The destruction of the Bush administration and the election of a Democratic President.
The first event must precede the second, but in order to do that, we need as many people/organizations going after G.W. as possible. So before you send your hard-earned money to John Kerry or the DNC, consider other organizations like Democracy for America or MoveOn.org. Do a google search and find a group of people who most closely follow your political philosophy and give donations to them. Republicans and conservatives have been doing this for decades, and we are just now playing catch up.
Consider the effect on the average undecided voter watching multiple television ads sponsored by different groups as opposed to the effect of one group or person sending a barrage of political messages to that individual's TV screen. I believe we will be more effective on the whole with this method. Continue to give to the candidate and the party, but reserve your more substantial contributions for your favorite groups. You will be much happier with your investment in the long run.
As a side note, I work for neither "Democracy for America" or "MoveOn.org" in any official capacity, although I do support both whole-heartedly.