My favorite is Allstays. I have the Passport America, Good Sam (GS Camping) and RV Parks apps (all on the iPhone). But I find Allstays to be the most useful. I think it was about $10 and worth every penny (IMHO).
2013 F-350 CC SB 2WD 6.7PS
2013 Eagle Premier 351 RLTS
-SOLD- 2012 X23B
-SOLD- 2003 Ford Expedition 5.4, Bilstein shocks