Protective cases, sleeves, and covers for tablets
Many kinds of protectors are available: sleeves, portfolios, cases, and covers. Choose one based on aesthetics and your usage patterns -- sleeves need to go somewhere while you work and are best suited as protection while in transit, for example.
I prefer the combination of a separate screen cover like the Apple Smart Cover and case such as Speck Products' SmartShell because I can put aside the cover while holding the iPad, reducing its weight. You won't find such magnetic covers for Android tablets, so your best option is a case designed for your specific model, such as the Samsung Book Cover. (I'm not a fan of screen films, as they're typically messy and not durable.)