Nothing is cooler than wireless charging. Here is a little known fact that even I didn't know until I came upon an awesome review by Droid Forums Moderator "MandyMakesApps", the Galaxy S4 is Wireless Charging "Capable" not Wireless Charging "Equiped". This bodes well for Samsung stock holders as this makes the purchase of their wireless charging back and wireless charging pad ($90) seem to be a pretty good buy. As Mandy stated I feel like there may have been a bit of deception in Samsung's marketing.
You don't have to shell out crazy cash to get wireless charging on your Galaxy S4. Apparently there is a stick on wireless charging receiver module by Qi that can be had for only $12. Once that is installed you can grab a used wireless charging pad on ebay for a reasonable price or use one that you already have.
Mandy has put together a great writeup on how all of this works and how exactly it is used. There are also some tips for how to apply this to your Galaxy S4! Check out her full writeup at the link below!
Wireless Charging on your SGS4 in 20 seconds.