Right now, it's slim pickings if you want a smartphone that supports Daydream VR headsets. Outside of Google's own Pixel line, you're looking at just a handful of devices from ASUS, Huawei, Motorola and ZTE. Your choices should get better soon, though. While discussing Google's financial results, Sundar Pichai revealed that there should be 11 Daydream-capable Android phones by the end of 2017. The Galaxy S8 is the first out of the gate (that update is arriving now, in fact), but that still leaves a few other handsets.
As to what those could be? Google's next Pixel phones are a lock, but third-party brands are a tougher call. A Daydream-ready phone has to meet specific display and speed requirements, such as a 60Hz refresh rate while in VR and sustained processor performance. Those targets are becoming easier to hit over time, but they still limit potential Daydream support to higher-end phones. It could take a long while before a budget phone can immerse you in virtual worlds.