Satoshi's bitcoind implementation bugs
I'll try to give a list of the cases I know of. Whether these are considered bugs or implementation oddnesses is debatable, I guess.


The genesis block's coinbase output cannot be spent.
The OP_CHECKMULTISIG and OP_CHECKMULTISIGVERIFY operations pop one element too much from the stack (requiring an extra dummy push in the redeem script).
The checksig operations in a coinbase's scriptSig count towards the sigop limit of a block, even though that script can never be executed.
Encoded public keys and signatures are valid if and only if OpenSSL accepts them, including the many non-standard or simply broken encodings it accepts. Since 0.8, such non-canonical encodings are considered non-standard, but still valid inside blocks.