can you recommend any free php scripts?

This is the top dog OpenX: Take control of your advertising | OpenX ......... donwloaded and played with it a couple years ago but din use it. Too good for me

Yup, very powerful and feature packed. I was looking for something much simpler back then

OpenX almost has no competition in terms of open source ad serving.

A notable competitor - Google just started their own solution (after acquiring double click): https://www.google.com/admanager

But now it is for invitation only.

Yes phpadsnew is the best one, but take care if you have high visted site (forum) on shared hosting.