If you have a lot of high-resolution photos, but you want to quickly resize them to a smaller size so you can share them more easily or upload them to a webpage, check out DropResize.
DropResize runs in the system tray and basically monitors a folder that you specify for new images and then automatically resizes them to whatever you height and width you prefer. It does keep the aspect ratio. As of right now, it only supports JPEG images, but the next release will support more.