The program that comes with HP's scanners and printers is also good. As is Photoshop or Paint Shop Pro. I use one of the 3 depending on what computer I am on but if you can keep smaller resolution (there is really no need for 600 dpi for the avg users like us - I mean we are not graphic artists, well speaking for myself anyway, lol). I agree with Marko- when you scan or take the pict, check to see what resolutution it is set at. Or change the res after.
But the 3 programs I have tend to let you keep the quality of the image when you resize it. And that works for me b/c it is not at all complicated and I'd rather program some complicated code than try to work with graphics, lol