- Google Maps (street, online)
- CoPilot Live (street, offline)
- Backcountry Navigator (topo/satellite, offline)
- OruxMaps (topo/satellite, offline), better in some ways than BCN but has limitation on size of downloaded area currently
An OBDII app...
- I use TouchScan, Torque is more popular
- a general document viewer for excel/word/etc like OfficeSuite Viewer (i have a list of OBDII codes in excel format)
- Adobe Reader for a copy of the factory service manual
Lux (lets you set the screen backlight much dimmer than normal for night time use, not necessary if you have certain custom ROMS though)
An automation app...
- these sort of apps let you do basic stuff like tell the tablet to go into airplane mode to save power when external power is disconnected, or advanced stuff like start an FTP server when your near your house based on which cell tower it sees.
- Tasker rocks, but it's got a steep learning curve
- AutomateIt has a much cleaner UI, but i've not used it personally
- llama is a popular free one, but a bit limited
A media player app...
- I'm using "PlayerPro Music Player" with the Holo ICS skin, works for music and video
Streaming media apps (if you have a 3G/4G connection or can tether to your phone)...
- Youtube/Hulu Plus/Netflix
Weather apps (if you have a 3G/4G connection or can tether to your phone)...
- i'm using HD Widgets
- i also have Weatherbug Elite for more detail
- a file manager, i like ES File Explorer better than ASTRO
- a backup app like Titanium Backup (not only making it easy to backup the entire config of the tablet, but also can get rid of annoying built-in apps from the phone company)
- maybe a task manager, but i rarely need it - depends on the device and the version of Android
i consider root access to be a minimum personally so i can do whatever the frig i want with it, but you don't NEED it. i actually like to run a custom ROM too, but that's definitely not needed.
in addition to all the above apps, i have my custom app for interfacing with the steering wheel buttons. i've also done a lot of customization with Tasker. finally, since i have root and am messing with behind-the-scenes stuff, i have SuperSU and Better Terminal Pro.