As equally as important as the screen protector, is the phone case. Do not skimp out and buy your $500 phone a $2 case off eBay. I personally like to use a rule of thumb for pretty much any property I buy under $1000; be prepared to spend 10% of the items value on it's protection. So with a $10-15 screen protector, you should be looking at a $35-40 case. I'd like to note that this is the retail value, as if you can get a $40 case for $25 on eBay, that still counts as a $40 case. In my mind, the most popular, quality driven cell phone case brand right now is Otterbox. I hear that a lot, and I have people asking me "is that an Otty?". I always reply with, "It's an Otterbox." The company mascot isn't Otty the otter! no more Otty! Back on track though, Otterbox makes a decent quality case, in several variations for a good number of popular phones. Their are a ridiculous number of case manufacturers out there, and I don't have the time or energy to list off even the top 10. I will however recommend my runner up to Otterbox. Trident Cases has caught my attention as they seem to offer cases that are very similar in specification to their Otterbox counterpart, but with a curvy, almost more flashy design. Trident seems to offer the same number of variations and colours as Otterbox, and I believe that they would protect your phone just as well. The big difference between Trident and Otterbox is the price. You can go on eBay and find a Trident case for $25, when it's Otterbox competition (of comparable stats) will be $35. If the case works as well, and looks as good, but costs less... isn't that a good thing?
Long story short, buy a case and a screen protector for your expensive pocket computer. Those cheap silicone and TPU cases off Amazon and Ebay will cover your phone, maybe even make it look pretty, but when your phone hits the cement you'll wish you had a quality case.