Betfair are offering odds of 13/1 that Labour will have the most seats.
I think this is a very good bet given the "peculiarities" of the electoral system.
If you look on the bbc election website you will see that even though the Conservatives have 34% of the vote - given the Lib Dems support - Labour only need 28.6% of the vote to achieve the most seats (but not an overall majority).
Ive had £20 on it and may have more later
Paul Keevil