Get any standard whey protein.
Don't buy any of the shite loaded with all sorts of extra crap. It's all marketing.
People bang on about X being better than Y, but the only real difference between brands is the taste really.

I'd recommend optimum nutrition gold standard. Or if you're on a tight budget, my protein or CNP.
All the above are tasty.

@nova: protein is an important part of any healthy diet.
Even if you don't work out, I'd recommend having a shake for breakfast. If you tend to put on weight, replace some of the carbs in your diet with protein and it makes it much easier to control your weight.
Protein also keeps you full for longer.