Everyone needs them, no one wants to make them. Many of the ones you can scrape from the internet are kind of lame and only come in one size.
Here are some basic spinners with Apple-like proportions, available in 24px-192px sizes, so you can have spinners at 24px, 48px, and 96px at retina and normal resolutions.
I'll be making some sized 16-32-64-128 in the near future.
Make those loading screens a bit more dapper, and always provide user feedback.
I've already created .gifs for the loaders (black on white background, white on black background). If you don't need to customize them, then you're good to go.
I didn't spend too much time optimizing for file size, so their footprint may be a bit chubby for your taste.
Everything should be broken out into layers. If you need to modify the background colors, there should be a background layer in each file. Change the color, and add it to each pane of the animation.
Currently, the frame rate of all animations is 0.5s, which might be a little speedy for your taste. Above 0.7s, though, it starts to feel a little slow.
MIT License.