you can find a first version of a web based blockchain explorer for Ethereum at http://www.etherchain.org
So far it just shows blocks, transactions and account balances. I am currently working on a contract explorer and to fully automate the blockchain indexing (so far the process is only semi-automatic and not fully robust).
The explorer is hooked up to the PoC3 development network and I will keep it always pointed to the most recent development branch.
If you can think of any additional features or find some bugs, please let me know.