My favorite is Hacker News Enhancement Suite
[1], for unread comment counts, voting on front page, highlight unread, inline comment, collapsible thread, etc.
1: https://chrome.google.com/webstore/detail/hacker-news-enhanc...
1: https://chrome.google.com/webstore/detail/hacker-news-enhanc...
I take pull requests at https://github.com/etcet/HNES but I only have a few hours a week to work on it.