-SimplyText and Mightytext: two sister apps, one of which syncs text messages across any device that is logged in with the account and that has the client (web client and tablet app available) and allows texting from any of the aforementioned devices, along with syncing and controlling some things (such as MMS, photos and allowing to pickup/hang up phone calls) while the other is (imo) a superior messaging app to the default one. -A compass app. I found one that requires absolutely nothing, and so if I find myself somewhere without Internet, I can always ask for a paper map and use that compass. -The app that gives me the schedules and warning for the local bus and subway service. -Kindle because free e-books -SwiftKey which is pretty much a free Swype. Not as good, but it's free. -Had to uninstall it because phone isn't as powerful as I would like, but IFTTT is a good conditional alarm system. -Alarmdroid for all of my alarm clock needs. -Wifi Analyzer because my neighbors have no idea what a WiFi channel is so I have to ensure that my router is always on the optimal channel (though might not be a problem anymore because now I can just increase the power output of my router because of DD-WRT)
+1 for mighty text. I use it all the time in my house because I only get service in the living room, not my bedroom (where I typically work) Not only can you send and receive messages from it, but you can read all notifications and see who's calling and so much more. It takes some fine tuning (ie: I don't need my mail notifications to show up on my computer because my computers mail app does that already) . I have the chrome extention so it shows up using Chromes notifications on my MacBook. Super nice.
If you want to have fun, look up United Remote - it's the exact opposite of Mightytext. Mightytext allows controlling your phone from your computer? United Remote allows you to control your computer from your phone.