Here are some useful extensions, scripts, and tutorials for Tumblr. Scripts require a simple, one click install for Google Chrome. Firefox users may need to download Greasemonkey first before installing.
As far as I know, these scripts/extensions can work together. Please note that I don’t personally make or use all of these scripts and tools, so I can’t help with any problems or issues.
I’ll add more links as I think of them, and feel free to share your own tips or resources.
Missing E - Probably the most popular Tumblr extension. Features: one click reblog/queue/drafts, automatically clears all tags when reblogging, adds tags to ask/reply, allows one click reply to comments, shuffle queue, adds timestamp to posts on your dashboard, replaces text (reblog, notes) with picture icons, and more. Downside: Tumblr apparently hates Missing E, and will try to scare you into disabling it.
Xkit - Similar to Missing E. Some additional features: Unfollower check, shorten long posts on dashboard, highlight key terms in posts, download mp3 from audio posts.
Tumblr Savior - Blacklist tags that you do not want to see on your dashboard. Downside: Not everyone tags.
Some selections from a larger collection of scripts:
Tumblr Life - Quick links to sort your dashboard by content (photos, text, quotes, video, etc), adds keyboard shortcuts.
Tumblr Hate - Do you keep seeing the same post reblogged in your dashboard? This script lets you “hate” that post so you won’t see it again.
Tumblr Helper - Create post templates with common settings, add personal notes to users on your dashboard
Notification eraser - Maybe you have one post that keeps getting a ton of notes and you want the notifications to stop showing up in your dash.