There are a lot of cases and sleeves out there for the Surface pro 3 of varying grades. Many times, I just need something simple that I can throw my Surface in, so it doesn't get hurt if I drop it on my way to a meeting or get beat up in my laptop bag. That means I generally opt for a cheap neoprene sleeve.
However, if you are in the market for a sleeve that is more rugged, makes a statement, or just plain looks great, then you need to check out WaterField Designs' Outback Sleeve for the Surface Pro 3.