I'm a bit behind in mentioning it, but Watermarker 2 is out. This Mac app from developer (and former MacStories writer) Don Southard lets you quickly resize and add professional watermarks to batches of photos. It's a great-looking app that elegantly accomplishes its goal.
You can use custom text, import your own logo or image, and apply a customizable strike-through "X" over an image (all with adjustable transparency). You can also add pixelation to an image to obscure parts of it, and annotate images with additional shapes.
Watermarker 2 offers powerful batch photo manipulation features such as renaming groups of files based on patterns and resizing using pixel or percentage constraints.
You can save your watermark settings as presets, and apply them to batches in the future with a couple of clicks. There's even an Action Extension for sending images from other apps to Watermarker, and a Share Sheet for sending watermarked images to others.