Not to many smartphones these days support microSD cards anymore. With Samsung also doing away with microSD card slots this year in their Galaxy S and Galaxy Note lineups, microSD cards haven't been selling as well as they had been in the past. While there are still a handful of flagships with them, they are becoming more scarce. If you own the HTC One M9, LG G4 or even the Moto X Pure Edition/Style, you do have a microSD card slot. These all support microSD cards up to 200GB (technically it's up to 2TB, but those haven't been invented yet).
Right now, Samsung is selling their 64GB EVO MicroSD Card over on Amazon for just $18.74. Now that's a crazy low price for a 64GB microSD card. These typically go for around $40 or so. If you have a smartphone or tablet with a microSD card slot, it's definitely worth it to pick one up. With this 64GB microSD card, you'll get around 59GB of usable storage. Still plenty to be able to store your music, photos and such on the card, and keep the space on your phone free for apps. Especially those that cannot be stored on a microSD card. You can pick up Samsung's 64GB MicroSD card from the link below.
Samsung 64GB EVO Class 10 Micro SDXC - $18.74