• Lemmyverse - Filter and find Instances and Communities
• Lemmy Community-Browser - Alternative site to search for communities
• sub.rehab - Find where your favorite subreddit has made a community onn Lemmy
• FediDB - View Stats about Fediverse and Lemmy Instances.
• The Federation - Stats and Graphs on Fediverse Growth and Popular Instances on them
• Awesome Lemmy Instances - Index of Popular Lemmy Instances
• Fediverse Observer - Another site to find popular instances
• Lemmymap - Size of Different Lemmy Instances Visualized
• fedi-block - Find which instances have blocked your home instance
• Fedisearch - Search Fediverse through various search engines

I also made a post collecting beginner guides for new lemmy users. Feel free to comment any new site and I'll update the list.