I understand some of you would prefer not to have to rely on a 3rd party service to discover the hash tomorrow.
One way to do this is to run your own client, but if you don't have geth already synced on the testnet, it will take 24+ hours, rendering the process moot.
A way around this is to run the C++ client, which syncs the chain in a record-breaking 4h30 on a core i7!
Instructions on installing the client can be found here: https://github.com/ethereum/cpp-ethereum/wiki/Installing-clients
If you can keep that node up and switch it to the livenet following getting the hash, even better - as you'll help contribute to the overall health of the network. Extra points for getting it getting it added to the netstats panel