I don't use GNOME much these days, but below is a list of some apps that I think can replace KDE apps. The problem is that usually they are not as feature rich as their KDE equivalents.
Amarok -> Exaile, rhythmbox, banshee
Ktorrent -> Deluge (or Azureus if you don't mind a gtk/java app)
Kate -> Gedit (although in my opinion its not as good or as feature rich as KATE)
Kget -> gwget
k3b -> gnomebaker (again I don't think its as good as k3b)
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