Note: I'm not considering KDE-based and Windows-only solutions. I may not consider GTK-only solutions as well.
Executive summary as of the moment: Despite its UI quirks and C++ only support, Qt Creator is the way to go. Monkey Studio with template additions is a credible alternative–assuming the debugger works. Netbeans + C/C++/Fortran isn't bad, but the odd project structure is off-putting.