The winning post is actually 323 MPs, not 326, since the five Sinn Fein MPs won't take up their seats, leaving the Commons at 644 MPs plus the Speaker. We're still waiting on Thirsk & Malton which has been delayed by three weeks due to the death of a candidate, but it's a Conservative safe seat so I shall count it for the Tories.
The only two-party coalitions that work are Conservative + LibDem (364 MPs -- pretty likely end result) or Conservative + Labour (565 MPs -- essentially a government of national unity, and not very likely).
An entirely right-wing coalition seems unlikely. The Conservatives and DUP together can only muster 315 MPs, and there aren't any likely candidates to provide the other eight votes. Maybe they could get the SNP and Plaid Cymru on board by offering pork for Scotland and Wales, but it would be very unstable.
A grand alliance of centre-left parties seems more likely, if the Conservatives and LibDems can't reach a deal. Labour + LibDem + SDLP + Independent Unionist + Green + Alliance Party -- that would be 321 MPs, and so would also need support from the SNP (or Sinn Fein, if they could be persuaded to take up their seats), but they're more likely to support a centre-left government than a Conservative minority government. I think Brown would have to go as part of the price for putting this together. I expect the smaller parties would not formally join the coalition, but simply agree to vote for the Queen's Speech and Budget.
In any case, I would give two years as the absolute maximum time before another general election, and I think another one this year is pretty likely.