I think some people are getting a bit ahead of themselves with all this talk of who might coalesce with whom and under what leader. Anything could happen, but it seems clear the most likely outcome at present is still that the Tories don't get an overall majority but do come first in seats and first in votes.
It remains entirely possible, and is I think quite likely, that David Cameron could form a minority government and brazen it out for many months if not years. The opposition parties may be in no position to mount a challenge for a long time -- especially since Labour after its defeat could well implode in recriminations and backstabbing. Also, nobody will want another election any time soon because the parties are all broke.
Naturally, I hope this is not what happens, but we need to keep our feet on the ground. People are forgetting that, historically, minority governments are not especially weird or unimaginable. We had one for nearly all the period 1974 to 1979.