No matter what its ultimate cost is, the economic recovery plan that Congress hopes to pass by Presidents' Day is going to be a colossal enterprise. Luckily for Democrats, their 78-seat advantage in the House is one of the largest in the party's recent history -- but challenges still await Nancy Pelosi and Steny Hoyer as they work to line up various factions of the caucus behind the stimulus bill.

Which of the intra-party factions are poised to exert the most influence over the recovery legislation as it takes shape? Here's a handy run-down of the groups in play.

The Blue Dogs: This caucus of fiscal hawks, founded in 1995, is dominated by southerners and centrist Dems. Their mantra is "pay-go", the principle that any new government spending should be offset by a corresponding cut elsewhere to bring the budget towards balance. As you can imagine, they've had a pretty dismaying run of late. But that doesn't mean the Blue Dogs won't, to use a popular pun, bark loudly if the stimulus plan isn't accompanied by hard promises of fiscal austerity down the line. This group may also join Republicans in putting downward pressure on the bill's overall price tag.

The Progressive Caucus: Co-chaired by Reps. Lynn Woolsey (D-CA) and Raul Grijalva (D-AZ), this group released their stimulus wish list in mid-December, with a focus on job creation, foreclosure relief, and a proposed new energy block grant to help cities shift towards a more sustainable grid. These lawmakers are those most likely to be pulling the emphasis away from tax cuts and towards the type of outside-the-box infrastructure projects that would help end the nation's dependence on dirty fuels. The progressives also are not shy about insisting on a $1 trillion bill. Unfortunately, they had slightly more members than the Blue Dogs at last count but their political pull, historically, is weaker.

The Appropriators: This faction is easily identifiable, lining up with the Dem roster on the House Appropriations Committee. Hill folk are fond of saying that there are really three parties in America -- Democrats, Republicans, and appropriators -- and this group's rarefied status as holders of the national purse strings is nothing to sniff at. Because their panel's job is mapping out funds for specific projects, the appropriators are likely to be the loudest advocates for targeted stimulus spending that might test Obama's vow to keep his plan "earmark-free."

City and Country Mice: Urban policy has been so neglected during the Bush years that Obama is setting up a special office for it, but that doesn't mean lawmakers from urban areas won't lobby especially hard for their priorities in the stimulus. Philadelphia's Rep. Chaka Fattah (D-PA) and New York's own Rep. Jerrold Nadler (D-NY) are already raising their voices for cities. Of course, lawmakers from rural areas are already positioning their localities to get special attention; good examples are Rep. Mike Thompson (D-CA) and freshman Rep. Ann Kirkpatrick (D-AZ), who's replacing corruption magnet Rick Renzi.