Are there any "App Store quality" apps for creating animated GIFs from a series of image files? I searched the App Store for "animated GIF" but the only returned app was one to convert a movie file into an animated GIF. I need to go the other way: I have a series of screenshots taken of an app that I'm a beta tester for. These are the standard PNG files created by OS X's ⌘+⇧+4 keyboard shortcut. They show the sequence of events I use to reproduce a display bug.

When I say "App Store quality" I mean they are native Cocoa apps. These apps generally have attention paid to user interface and usability. You know, all the things that make good Mac apps good.
You might install ImageMagick with brew install imagemagick and then use something like this:

convert -delay 4 *.png output.gif


-delay 4 sets the delay between frames to 0.04 s.

See http://www.imagemagick.org/Usage/anim_basics/ for more information.