This article from the UK Polling Report is actually a much better guide to what might happen next than I could ever do, seeing as how it contains actual facts.
I think this bit is interesting:
The second issue is the Liberal Democrat party’s rules. Formally Cameron and Brown have a free hand in negotiations, Clegg does not. The Southport Resolution in the Lib Dem rules requires him to get the support of 75% of the Parliamentary Liberal Democrat party, and 75% of the party’s Federal executive (and failing that the support of two-thirds of the wider party) in order to enter into any agreement that “could affect the party’s independence of political action” – taken as meaning a coalition agreement. While all the leaders would in practice need to take their parties with them, only Clegg would have such a formal process to deal with somehow.