I like to keep a backlog of items I want in my Amazon wishlist, then when I go to buy something and I'm just short of the free shipping, I have a few items I can add. They are usually books that easily get me over $25. I also keep a wish list at Newegg, but I don't take the time to create wish lists at all the site I visit.
Enter Amazon's Universal Wish List. By adding a "favorite" to my web browser, with one click I can now add items from any site to my Amazon wish list. Now I can centrally manage the things I want, waiting for the right price or occassion to buy.

You can see in the image above that I've added three items to my wishlist, two of which came from another site. On the item's page, I simply click on the "Add to Wish List" button on my Favorites bar and a small window pops-up asking me to enter comments and verifying I want the item added. Then when I visit my normal Amazon wish list, I see the items there.