We use 1.75mm PLA in a variety of colours.
Stock colours are Black, White, Grey and Orange
PLA, or Polylactic Acid, is a biodegradable plastic with a lot of features that make it great for 3D printing -- it doesn't give off fumes like ABS does, or warp nearly as much. It's also really shiny.
PLA is harder than ABS, but more brittle, but that doesn't mean that it's easily breakable -- it's actually super strong -- just that when it does give, it's more likely to snap than bend. And it also stays flexible for a short while as it cools, which can be handy. And it doesn't warp and crack on larger objects the way ABS can. Basically, each is better for different kinds of things, and getting comfortable with PLA will give you choice and flexibility.