No Lock - I'm not a huge fan of screen lock, especially Casio's iteration.
Go Launcher EX - Gets rid of the excessive menus and slide out menu. Themes.
Go Calendar widget - Syncs with Gmail. Provides silent notifications in the status bar.
Go TaskManager widget - Has a 'clear' running processes button as well as a 'refresh', can access running processes with a touch & hold.
Go Keyboard / Gingerbread Keyboard - Currently trying out Go, however it consumes 5x the resources of Gingerbread Keyboard, may revert.
Juice Defender - I like how I can set it to manage my Wifi connections and data connection.
BeWeather - It fetches weather data from wunderground.com ---my preferred source. It presents data conveniently for me, and I am usually always interested in wind forecasts. It has weather advisory alerts.
Go Weather is a free option that also fetches from wunderground.com
PowerAMP - Full-featured media player to replace the original one.
YAAIC - Lightweight IRC program. Originally tried AndChat but I couldn't toggle off vibrate notifications for server disconnects = too annoying.
Opera Mini - Web browser.
Power Widget - More power options.
Astrid - Task manager, as in a check-list.