I have to say, I think a Lib-Lab coalition would be a bad thing in the circumstances. The Tories would vote down all tax rises and progressive legislation, while standing aside for spending cuts. Meanwhile, the coalition would have to spend all its time proving to the markets that it's macho enough to cut spending. We'd be like America - 'nuff said.
Far better to let the Tories form a minority government. Then Clegg can wake up every morning and think 'what ransom can I extort today?'