Short version: House Republicans are spineless, backstabbing bitches.  And that's coming from someone who thinks the proposed bill was terrible and should have failed.

From the perspective of lawmakers, there's a classic collective action problem.  Every Congressman (with the exception of the diehards like Kucinich or Paul), has been convinced that the bill is necessary.  However, they also know that it's exceedingly unpopular with their constituents.  The optimal outcome for any individual congressman is the same: the bill passes while they vote 'No' and then run on it.  This is what Congressional Whips are for.

However, there's a bigger problem.  If either party can get away with letting the majority of their members vote against it, then they all benefit, since the party can run nationally against it in 2010.  So Speaker Nancy Pelosi and Majority Leader Steny Hoyer met with Minority leader John Boehner to come up with a scheme to get the bill passed without endangering their incumbents.  The members of the party with the safest seats would vote for it, letting the 40% who were in trouble safely vote against.  Each party would deliver 50-60% of their membership, keeping either side from getting demagogued badly for something that they both believed necessary.

Pelosi delivered: 60% of Democrats voted for the bill.  33% of Republicans did.  Boehner apparently screwed up his count, since if he had delivered a few more he might have been able to get it passed with majority Democratic support.  Keep in mind how cynical this is.  He (and the rest of the caucus) believes this bill is absolutely essential for the health of the American economy.   But he was perfectly willing to promise support, then stab the other party in the back by voting no at the last second, panning to run against 'the 700 billion dollar giveaway to corporate fatcats' in 2010.  And what was the figleaf given for the betrayal, the willingness to sink the economy?  Nancy Pelosi was mean to Republicans in her floor speech. 

So where does Congress go now?  I'm reminded of an ancient fable.  During wartime, a Greek king was holding court one day when a mystic showed up with twelve scrolls of prophecy that held the key to winning the war .  After proving that they were perfectly accurate, she demanded a staggering sum of gold for them.  The king refused, saying that they weren't worth that much.  So the prophet grabbed a nearby torch and set one of the scrolls on fire.  She then repeated the same price for the remaining eleven scrolls.  Again, the king refused.  So once more she incinerated one of the scrolls.  This continued until after burning the sixth scroll, the king gave in and paid the full price.  Because he knew it was necessary.

EDIT: Just in case you don't believe that they're really that bad, the Republican National Committee already cut an ad against the bailout when they thought the vote was going to succeed on the backs of Democrats.