Eligius is the first pool to support OP_EVAL-- thanks Luke-Jr ! Block 155974 is the first "I support OP_EVAL" block in the chain.
The pull request for the next version of bitcoin is ready to go:
https://github.com/bitcoin/bitcoin/pull/669
... and there are backports of just the changes relevant to mining available at these git branches:
https://github.com/gavinandresen/bitcoin-git/tree/v0.3.23_op_eval
https://github.com/gavinandresen/bitcoin-git/tree/v0.3.24_op_eval
https://github.com/gavinandresen/bitcoin-git/tree/v0.4.1_op_eval