DigiKam is the best programme for this without going to the GIMP which is a
full blown editor. I would also look at Krita and Shotwell. The first two
are parts of KDE but work in Ubuntu (GNOME) just fine. Shotwell has replaced
F-Spot in Ubuntu 10.10, but it is alaso available for Lucid. You could try
Picasa, but it is not a native Linux application. It uses Wine libraries to
work and it can be slow, IMO. There is also a Nautilus action that you can
add in the repositories that will do this from a right click in the file
manager.