As mentioned below, Q1 is the low-hanging fruit. One key nugget, as the data starts coming in (and campaigns don't have to report until the 15th), is how many individual donors each campaign had. I'm willing to bet some correlation between those numbers, and the campaigns who can keep up a strong fundraising pace.
Hillary Clinton: $36 million, 50,000 donors, includes $10M transfer from Senate campaign
Mitt Romney: $23 million
Rudy Giuliani: $15 million
John Edwards: $14 million
Chris Dodd: $9 million, includes $5M transfer from Senate campaign
Bill Richardson: $6 million
Joe Biden: $4 million, including $1M transfer from Senate campaign
Note, not all this money is available for primary races. A further breakdown when campaigns report will determine how much is primary money and how much is general election. Donors are allowed to give $2,300 for each. $1 million of Edwards' money, for example, is general election money. A sizeable portion of Giuliani's money is as well, supposedly. All of Romney's money can be used in the primary.
Nothing yet from McCain or Huckabee (who has fallen off the face of the earth). And what about Obama? Is he holding back to make a splash surprise announcement? It wouldn't be a bad idea to play coy for an extra day if he's got huge numbers to report.