Reddit unfortunately. Every so often I'll search for a topic online and in the related posts/communities section I will find an obscure one and just see what the top voted posts are
Post it here on Lemmy! So then in 2030, when someone on that hot new social media app, PoopMouth asks this question, and Reddit becomes dead as Digg, they can say they find memes on Lemmy.
I did not see it mentioned so I'll add: meme generator on imgflip. It's probably easier to just make your own, but that one works from a mobile phone:-).