We believe this should be part of the operating system… so here you have a couple of solutions
1. resize
a) use preview
basically you have to open all the items in Preview and select them all and then change the image size. An explanation can be found here http://mac.tutsplus.com/tutorials/os-x/3-easy-ways-to-batch-rename-files-on-the-mac/
b) use a command line sips
This powerful command line script coming from BSD is very powerful and simple to use.
http://petapixel.com/2012/11/21/how-to-quickly-resize-multiple-photos-on-a-mac-using-a-terminal-command/
2. rename
Following this review http://mac.tutsplus.com/tutorials/os-x/3-easy-ways-to-batch-rename-files-on-the-mac/
We decided to use namechanger
3. optimize
Following this review http://best-mac-tips.com/2012/08/15/best-resize-images-mac/ and use ImageOptim
HolaRails 
For a simple to use drag-drop batch resizing tool, I develop an app called ImageXY (www.imagexyapp.com). If you are resizing lots of images or resize to specific sizes often then it is a lot faster and easier than using preview or the command line…can resize 100 DSLR photos to web size in ~5 seconds.