Is there a way to use the block chain as entropy in random number generator? I want to create a transparent gambling/lotto site and use the block chain as entropy for lotto numbers, dice rolls, that kind of thing.  Would the transaction hash of the latest transaction be the best way to do this?  How often are transaction hashes created?  How would you, programmatically, access them?
The Bitcoin Lottery used an SHA256 hash of the two most recent blocks to generate random data and to my recollection there were not too many complaints about that method they chose. In any case it's only good for 256 bits of questionably random data every 10 minutes (20 if you don't reuse blocks) so there are probably better entropy sources, such as the setup they've built over at random.org