Some good advice given out so far.
Here's mine, for what its worth.
I have quite a few images on my system and I have to say that if it weren't for my image management software, I would definitely have a big mess on my hands.
There are 2 software packages that I'd like to recommend. They are not image editors but more image management and manipulation. They can't do what Photoshop can do but they don't need to.
What is cool about both programs is that you can resize multiple images all at once. Not only can you resize a bunch of images all at once you can adjust the brightness, contrast, hue, etc. all in one fell swoop. Makes it a whole lot easier than doing each image, one at a time.
One other reason people resize their pics is so that the image file size is smaller as well. Just be aware that depending on what program you use, even though you resized a picture, the image file size can still remain quite large. For example, say you have an image file whose dimensions are 1600x1200 with a file size of 500kb (.5MB). You go to resize it in Microsoft Imaging to 640x480 so you can email or post it to a website. After resizing it, the file size has gone from 500kb to 240kb. Yes the file size is smaller, but for web or email the ideal file size for a picture whose dimensions are 640x480 should be around 30-60kb. When resizing in either program you can adjust the resolution quality of the pic so that when it gets resized the file size drops significantly as well.
The 2 programs I've used over the years are:
ACDSee
and
Thumbsplus
Both are well worth the money and you can download demo copies to try before you buy.
To keep your images organized they are a god send.
good luck!
Jel