Each photograph I download from a memory card is automatically renamed with the date and time the image was shot. For example: 20060623_140123.jpg says that the photo was taken on June 23, 2006 at 2:01 PM (and 23 seconds). Each time photos are downloaded from a card, they’re put into a unique directory named after the current date. If I do more than one batch per day then a batch number is appended. For example: 2006_06_23 or 2006_06_23_01. For events or special occasions I’ll append a description to the folder name. The image download software that came with my Nikon does all of that for me but it wasn’t the default. Most image download software will allow you to do this and more.
It’s a nice naming system because each photo gets a unique identifier and it makes it easy to find the actual photo given the name or the date when you remember shooting it. Having a unique identifier for each photo is important if you’re selling prints since it allows your customers to tell you exactly which photo they want to buy without any misinterpretation (and if you’re licensing them for use you can put that ID in the license).
I’m curious how you name your digital photos? Is there a way that works better for you?