Lock Laces are advertised with the slogan "Why Tie, When You Can LOCK?". They are elastic laces that you just tighten and lock in place with the clip. You can see in this video how quick and easy that is.
When I see people double-knotting their shoes, or stopping mid-workout to retie their shoes, I always suggest Lock Laces. Many times people say that double-knotting works just fine, and maybe it does, but even double-knotted laces sometimes come untied.
But even though that's why these are advertised, that's not actually why I like these so much. When I run longer than an hour, my hands always swell up. After a half marathon, especially in warm weather, my fingers are sausages. I can't untie even a normal shoelace, much less a double-knotted one. But as you can see in this video, I can undo these and slip my shoes off easily, and not have to wait until my hands are back to normal.
These are also nice if I need to adjust how tight or loose I have my shoes laced mid-run. Try doing that with double-knotted shoes.
Lock Laces are about $8 in stores, and you can find them at Dick's and at any local running store. I've found the running stores usually have a better selection of colors. Since I tend to buy two or three of the same shoe at a time and rotate them, different colored Lock Laces help me keep track of which pair is which. You can also order them from www.LockLaces.com. I have not ordered from the website, but I have contacted Customer Service via email once when I had a product question, and they responded to me the very next day.