FreeSizer is an easy-to-use tool for quickly resizing (and optionally reducing the quality) of multiple JPEG images.

Simply drag and drop your chosen pictures onto the program, choose a profile which matches what you're intending to do with them (send the images via email, upload them to an iPhone, share them on a social network, and so on), click "Start Resizing", and FreeSizer will handle everything else.

By default the program will adjust the resolution and quality settings to match those in the profile you've selected, saving the resulting files to the same folder as the original images. Doesn't suit your needs? The Settings dialog allows you to have the images saved wherever you like. And it's also possible to set up a Custom profile with your preferred resolution and JPEG quality settings.

FreeSizer can save you plenty of time, then, but if you use it regularly then you may find RoboSizer (a commercial program by the same developers) even more useful. This detects when you're sending images via email, uploading them to the web and so on, then steps in and resizes them for you, all entirely automatically so you have nothing to do at all. The program is yours for $24.95, and you can download a 30-day trial version here.