Want to know exactly, where your photos were taken?
Don't want to spend a fortune?
If you own a relatively new smartphone, chances are very good that it natively supports geotagging of the photos taken by its camera.
But you need to meet a couple of demands!
E.g. a HTC Sensation telephone (announced April, 2011) will geotag your photos - IF:
Check your smartphone camera's Features to see if it supports geotagging! If "yes", you don't need to worry about installing any 3.rd party app.
From smartphone to DSLR
Use the GPS coordinates from your smartphone to determine, where the photos taken by your real camera were taken. If you feel like, update the pictures' EXIF data with the coordinates from the smartphone.
What is Geotag?
Geotag is an open source program that allows you match date/time information from photos with location information from a GPS unit or from a map.
Here is an example of a map showing a lot of places where photos were taken, and the description of each location.