I would recommend the Image Processor. It is available in PS with "File>Scripts>Image Processor" and in Bridge with "Tools>Photoshop>Image Processor".
Russell Brown also has a slightly more advanced version of the Image Processor available on his site called "1-2-3 Process". You can download and use it for free. It is part of his "Services" for CS4.
<http://www.russellbrown.com/tips_tech.html#DrBrownCS4>