Just heard - in a very round about way - that Penguin are accepting unsolicited manuscripts by email for three months. Haven't seen this on any literature/writing websites so perhaps they aren't promoting it in fear of drowning under an avalanche of words.
The following is from Penguin's website. You can also click on the title of this post to go straight there. Good luck!
Our company policy is to not accept unsolicited manuscripts or synopses and we cannot enter into correspondence about unpublished work. However, for a limited three-month period from the beginning of August until the end of October 2010, we will be inviting submissions to be sent in electronically to the following address: firstname.lastname@example.org. We ask that email submissions comprise a brief covering note and synopsis and not a full manuscripts. Please do not send attachments, please write out your cover note and synopsis in the body of the email. We remain unable to accept hard copy submissions and will not return or be responsible for the safety of any that we do receive, so please do not send any original or hard copy manuscripts to us. We will not contact you with feedback on your submission and will only enter into email correspondence with you if an editor within Penguin is keen to progress your idea.