Others 23 (including 8 DUP and 3 SDLP)
In this scenario the Conservatives would try to get support through either a formal coalition (as in the last government) or by "confidence and supply" agreements with other parties. This looks unlikley to work:
Conservative + Libdem + DUP + Lady Hermon (Ind) = 316 (10 short of the required 325, 7 short of the 323 that could technically form a majority without Sinn Fein MP's sitting in Westminster)
Labour would then try, but have a harder time at forming a majority:
Labour + Libdem + SDLP =296 (29 short, assuming the Libdems would speak to Labour at all)
If Labour does not do a deal with the SNP then David Cameron, as the leader most likely to be able to get close to a majority, will stay on as Prime Minister to see if he can get a Queen's speech passed. If he can't then he will probably give way to Labour and let them try.
At this point Labour will either do a deal with the SNP or we will head into a second general election in September.
One warning though: there is a nuclear option. If both the Labour and Conservatives believe that allowing the SNP any influence would be either too toxic or give them unnecessary credibility they might decide to form a "grand coalition" or "national government" with Labour and Conservative parliamentary parties forming one bloc in parliament. With Labour likely to be decimated in Scotland the effect of any fallout on Labour north of the border would be self limiting, making this scenario less unlikely than a few weeks ago.
And one final word on the general election campaign. The BBC Poll Tracker shows us that nothing that any of the parties did changed the outcome. Most minds were made up long before the campaign started: