For our many members who are data hoarders and find the 16GB version of the Samsung Galaxy S4 will just not cut it for you, you might want to check out AT&T's latest tweet, (assuming you are with them or plan to be). They just shared that their 32GB version of the device will be coming on May 10th and will retail for $249.99 on contract.
Of course, if the 32GB version still isn't good enough for you, eventually Samsung will offer the 64GB version, and we will try to update you when it becomes available. Either that, or you might want to re-evaluate your addiction to stored media... *long pause*... nah!
Source: AT&T