Apple TV RSS Plugin - Configure and read various RSS feeds right on your Apple TV.
ATVLoader - Install many plugins from a large database. This one is great for those that want a simplified and easy way of installing plugins without a lot of hassle.
nitoTV - The biggest and best plugin of them all. Network and USB mounting, mplayer, and DVD playback with VIDEO_TS files or ISO files.
Road Trip - GPS plugin that works with any USB GPS adapter, fetches maps from MapQuest.
Sapphire - Best way to manage TV Shows and Movies.
Sports Scores - This plugin allows you to check sports scores.
Streamer - Stream internet radio through your Apple TV.
MPDControl - Control your MPD server easily from your Apple TV.
ATVTorrents - Finds torrents in your Home directory and automatically starts downloading them with rTorrent.
Firefly - Allows the streaming of music on your Apple TV to iTunes.
Omelette - A fun puzzle game designed to run on your Apple TV.
Perian - Although not truly a plugin, Perian allows playback of many file types.
JamanTV - Download movies from the JamanTV service onto your Apple TV.
ATVWakeOnLan - Wakes up remote media servers nearby.
Applications Menu - Run applications on your Apple TV easily with this launcher.
Firefox - This hack shows you how to get Firefox up and running on an Apple TV, step by step.
Component to RGB - How to convert from component to RGB for TVs that don't have component ports.
How to Play DivX From a NAS - Explains how to play DivX files on your AppleTV from a network storage device.
Color Output - How to easily get color output from the AppleTV's component ports.
Asterisk - How to get Asterisk running on an AppleTV.
Keyboard/Mouse - How to get a USB keyboard and mouse working on an Apple TV.
Mouse Pointer - This tutorial explains how to enable the mouse pointer.
OS X - Install OS X on an Apple TV.
USB Drive - A tutorial that tells you how to boot your Apple TV from an external USB drive.
Enable VNC - Tutorial explaining how to enable Remote Desktop/VNC.
SSH and AFP - Explains how to enable SSH and AFP on Apple TV. (via)