I was looking for an application to easily resize multiple photos at the same time in a batch the other day and came across many different ones that were useless to me. I stumbled my way and the internet and I found Fotosizer. This is the best one out there and can do many things like change the quality, change the size, and even put them all in a different folder. I have had great experiences with this so far and I highly recommend it to anyone who needs to get the same job done.
It is a freeware app I recommend donating some money towards it. Go and download it here.