I've found digikam ( http://www.digikam.org/ ) to work pretty well. Never really cared for iPhoto though.
Keynote, again never really used it. I hear it's much nicer than the MS equivalent.
The wife likes GarageBand and it does seem to be a pretty sweet app. Not really sorta thing so I don't really know of any replacement for it. Audacity is the only thing that comes to mind and it's not exactly the same kinna thing.