http://galarina.squarespace.com/geotagr
I have an Eyefi card but it geotags using WiFi so generally only useful in urban areas.
This app (apparently) records where you've been and adds the info to your photos uploaded from cameras to Flickr - which is exactly what I want it for.
I'm aware that some people have a separate 'logging' device for this, but a phone app is simpler/cheaper.
Anyone use GeoTagr or similar?