Evan (@emschwartz) came up with this idea we sometimes refer to as Fishchain. The idea is that you can request a packet of data by broadcasting a payment where the condition is the hash of that data.
Not sure if this new or not, but I just noticed that the Fishchain idea works not just for message retrieval bounties as stated above, but message delivery bounties as well.
Imagine A wants to deliver a message m to B, but doesn't have a direct connection. C has a way to talk to both A and B, but doesn't want to relay a message for free. Neither A nor B trust C.
A could tell C: My buddy, B, will pay you 5 cents if you deliver my message to her.
C thinks that that is a fair price, so she first gets A to sign the hash of the message H(m). She then contacts B saying that she has a message for her whose hash is H(m) and presents A's signature over H(m). B promptly creates a transfer to C using H(m) as the condition.