Side/form a coalition, With the Conservatives
This naturally goes against the liberal ethos, obviously. But, imagine if they didn't go with them, consider the tories were the party with the most votes. And that's pretty much the core of democracy. Imagine how much the media would slaughter the "rainbow coalition"
Side/form a "rainbow" coalition, with Labour
Claim no allegiance
This leaves the country in a sort of no man's land until another election (Or whatever other bureaucratic stuff)