Automated or manual? If you want automated, do it through the sendmany RPC command in any recent version of the Satoshi client. If you want to do it by hand, the GUI in Bitcoin-Qt can do that on the send payment page.
Manual for now - so your saying the desktop top bitcoin has a send payment page to drop in a bunch of payment address's?
Hmm.. Well, from what it sounds like you're trying to do, perhaps the sendmany RPC might be better if you just have a list of addresses and they're supposed to get the same amount.