Post Your useful iPhone apps here.

Found one for Bangkok Thailand. Bangkok BTS/MRT map. This is a map for the skytrain and subway. It also tells you abut the various stops.

Here is what i use to travel:
-FlightTrack Pro.
-XE Currency
-Lonely Planet Thai Audio Phrasebook
-Filipino for Beginners

Some other useful "travel" apps:

Packing (build customized packing lists)
Four in a Row (practice so you can beat the bar girls)
Sudoku (for long airport layovers)

Map App:
MyMaps
It links to your Google Map 'My Maps', via your GMail account.
I just copied a Medellin Casas map from a post into my own maps, and added some extra places not covered, but documented in Blazer's MDE report.
I will get a Comcel Sim with 3G and casas here i come !

Zen, please elaborate. I'd like to put a SJO brothel map in...

There is some link:

http://my-maps.appspot.com/
http://itunes.apple.com/ca/app/my-maps/id321930101?mt=8

You build the map in Google Map on your PC, you need to have a gmail account. So the "My Maps" are stored in your account.
You then create the all the spots in a map named "SJO Casa's". Then you can share it and send the link.
Then we can copy your shared map using this procedure:
http://adlr.info/mymaps-iphone.html

You giving us a cool map would be awesome !!
Zen.

This is the procedure i used to copy a map, forget the other one...
http://sites.google.com/site/gmapstips/copy-move-features-between-my-maps

Icarus built a map i have copied, and added some more:
http://maps.google.com/maps/ms?hl=en&ie=UTF8&msa=0&z=13&msid=200421415499379545726.000497393777eab152395