ImBatch is an interesting batch processing tool which can convert, resize, rotate and carry out other operations on lots of images in a single operation.
Adding images is as easy as dragging and dropping them onto the program, and ImBatch supports plenty of file formats: BMP, DIB, RLE, TIF, TIFF, FAX, G3N, G3F, XIF, GIF, JPG, JPEG, JPE, JIF, PCX, PNG, TGA, TARGA, VDA, ICB, VST, PIX, PXM, PPM, PGM, PBM, WBMP, JP2, J2K, JPC, J2C, DCX, DAT, PSD, WDP and HDP.
Clicking "Add Task" then allows you to choose exactly what you'd like to do with these files. The options available are "Save As" (convert format), "Resize", "Rotate", "Soft Shadow", "Flip", "Round Corners", "Convert Colours", "Convert to Gray", "Set Tag", "Remove Tags" and "Shift Time" (the final 3 all relate to EXIF tags).
As you combine these tasks, so a Live Preview window shows you what they'll do to your target image.
There's even a task command to upload your processed images to Facebook, so you won't have the hassle of doing this manually.
ImBatch provides plenty of image batch processing power, yet remains fairly easy to use.