I've been using Google's Picasa to organize my ever-growing digital photo collection, and have found this to be one of the most intuitive and feature-packed photo management software ever created. And best of all, it's free.
Here're some of its features:
One of the features that I like the most is the ability for you to edit your photos while being able to retain the original ones. This means that when you edit a photo (maybe changing the brightness/contrast, adding texts, etc etc), you do not need to save the changes as another file. Picasa will remember the changes you made, but not apply the changes on the photos you've edited. You can however apply the changes by exporting the photo from Picasa. This gives you peace of mind when you're correcting some of your photos.
Don't just take my word for it. Download it today and see for yourself! You can download by clicking the Picasa button on my sidebar ---> :P