Being online every day I have a slight issue as a designer. I can't keep a traditional visual diary very easily, unless I print every image or colour scheme I like out; which I don't want to do in order to save paper.
On the Mac at home we use LittleSnapper to keep track of cool images and stuff, but I'm on a PC at work, and also use more than one machine. One day I came across Image Spark and I was very happy! It also has a Firefox plugin so that when you find an image you like, you just right-click and voila - it's now in your Image Spark scrapbook. Now that I've been using it for a while, I'm starting to see trends coming up in my choice of images, my style :-)