Kos makes the case for early money. I won't tell you who to donate to right now, but am instead making the case for donating "now" rather than later.
Judging from past experience, as we get closer and closer to election day '08 donations from readers will keep increasing. It'd much much much better if everyone sat down and figured out how much money they expected to donate to congressional candidates over the cycle and then figured out how to give as much of it as early possible.