has a number of good things and the quality is generally very good. Though there are very few cartoons on the site. Most of what they have is Anime and movie caps. Pic related, found it on this site. Also it seems to be fairly frustrating to navigate.https://animationscreencaps.com
This is probably the best site around for screencaps at the moment. Generally good quality and a decent variety.
There are a few other sites and tumblr blogs dedicated to screencaps. Though most are either very old, very low quality or both. For most things you are probably better making your own caps. Many video players even have a built in screen grab function.