http://picmarkr.com/ is a free website you can use to watermark up to 5 images at a time. (You are limited to 25MB at a time).
PLUS, there is an option to resize the images at the same time. You can choose 500 pixels, 800 pixels or 1024 pixels.
Once you have uploaded the images, you can watermark with text or an image (your logo). It then gives you 9 locations on the picture to place the watermark. (Top left, top center, top right, etc.) If that weren't enough, there are options on text color and opacity.
Check it out. This site can be a real timesaver. I love the ability to do up to 5 pictures at once.