I used to use fvwm as the window manager under Gnome 2, but as I understand Gnome 3 can't be used with a non-default window manager, so I'm looking for alternatives. Are there other desktop environments that have the option of switching to a different window manager?
Not all distros are made equal, particularly if you're a KDE user. KDE has had something of a rough time over the last couple of years. The transition from version 3.5 to 4.x hasn't been easy, and over this period many distributions have decided to use either Gnome or stick with KDE 3.5 as their default desktop.