gtkpod is a platform independent GUI for Apple's iPod using GTK2. It allows you to import your existing iTunes database, to add songs/directories/playlists, to edit ID3 tags, to modify the iTunes database without the iPod connected and to synchronize at a later time. gtkpod also features international charset support for ID3 tags, detects when adding already existing songs, and more.
New features include the stable sorting of displayed tracks (click several headers in order and have the view sorted accordingly) and the sort-ignore-lists (ignore the 'the' at the start of albums...). If you speak Hebrew, you will probably welcome the new Hebrew translation catalog.
More important for some users may be the support for iTunes 4.9 and firmware 3.1 released by Apple at the end of last month. Podcasts are still not supported, however.
The handling of dangling files (files referenced in the database but no longer present on the iPod) has been improved: after iTunes wiped most of my tracks from the iPod I felt it was necessary to touch that code and was thus able to restore the contents using an older backup database. And if you had problems getting the On-The-Go-Playlists to work correctly, this should have been fixed now too.