How to Organize your photos...?

I should have started some type of organization a few years back....I only have my photos on the computer by date. Is there any good way for a cross reference, perhaps where or who is in the picture, to somewhat have an organized photo collection?

Unfortunately, I must have 100 gigs on my external drive so the job my be a bit over the top, but would like to begin somewhere!

The files are basically Canon, so they are essentially IMG_xxxx. Any suggestions would be greatly appreciated
thanks
Rick
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