It can be difficult to find a publishing house that accepts unsolicited manuscripts. I can't count the number of times I've read 'we do not accept unsolicited manuscripts' or 'we will only read manuscripts which are sent via an agent'. Here are links to publishers who are willing to give both new and emerging authors a chance:
Allen and Unwin - The Friday Pitch
Pan Macmillan - Manuscript Monday
Penguin Books - The Monthly Catch
Harlequin Mills and Boon
So if you've got a manuscript looking for a home check out the above guidelines - good luck!