Lately I think Skype is the shit, I think video calls on cell phones is pretty rad

Not that it's anything new, shit my old dumb phone had a video chat option, but the quality now....it's just as good as the computer, kind of shocked me.
Emulators and roms are perfect for the old school gamer, then again you kinda need the right phone to enjoy them (xperia play), or a wii remote to bluetooth to.
Root explorer for root phones, explorer for non rooted, great file manager.
systempanel lite is a great task manager, works well for keeping track of specific app cpu usage, ram usage etc.
torch is a great app if you have an led on your phone, so handy when you randomly need a light, especially with the widget option.
Widgetlocker allows you to place widgets on your lock screen, as well as change the unlock slider to a custom one.
One punch notes is a great note program with good widget support, I never forget anything now.
Launcherpro is an amazing alternate home launcher if your looking for something customizable to the extreme.
Kami retro is a good game I recently got, was free when I got it. Great one for touch screen only phones.
Skyforce reloaded is a good top down airplane shooter. Reminds me of the old arcade games.
And there's many more depending on your interests. I didn't mention most games I have, as I can't imagine playing them without a gamepad.