I was recommended this program which resizes pictures in batches rather than having to do each individual image which is very time consuming!
In the 'Output' section, I reckon a JPEG Compression Factor/setting of 25 should give a good compromise of image quality and filesize. I did a test with it set on 1 and the filesize was 270Kb (down from 4.5Mb) and on 25, the same image had a filesize of around 70Kb with very little noticeableloss of image quality. Great for forums and web pages!
click on this link to download; http://www.virtualzone.de/files/resizer.zip