If you're looking to waste a few minutes online (or an hour) and you like guns, I've got the perfect site for you. Developed for airsoft no doubt, Dr. Noob provides the ultimate fantasy for most any gun build. They even have a full assortment of Magpul furniture, Troy hand guards, battle sights, and most other popular AR accessories to play mock up with.
It's actually a pretty nice tool to see a virtual build of your gun with various accessories before you lay down the cash for a new set of rails or optics. That way you can verify that your new set up will be tacticool before you even install it. The above image is a snapshot of my future build.