This is really simple to do with a script that talks to bitcoin to send a payment. Can probably even use cron or if you're on Windows the task scheduler for this.
Another possible option that is possible with the bitcoin protocol: if you want to pay someone every month for a year, you can send out 12 transactions, each with an increasing locktime that contains the time you want that transaction to confirm and the receiver to be able to receive those coins.
For this to work, you need to have the bitcoins up front, but it can be handy for instance if you want to pay for services from someone and don't want to give that person all the bitcoins at once out of fear of him/her running away with them.
Waldschrat: OT is open-transactions. I'm not exactly sure what it is yet as I haven't spent enough time reading up on it, but this post
by fellowtraveler may be interesting to you.