Here are the ones I use:
- Yelp
- RoadTrippers
- AllStays
- GasBuddy
- Yahoo Weather
A few new ones that look interesting:
The Waze app is also interesting - it let's people report accidents, dangerous road conditions, traffic, police, etc. But Google just bought them last year so it's starting to show up in Google Maps as well.
Joining various Facebook groups is also a great way to connect with people quickly about either certain areas/states/regions or certain topics like RVing or camping. I typically get some pretty quick responses back for questions like "I'm gonna be in this area for X amount of days, what should I do?".