Hi,
Something exactly like kde doesn't exist for fluxbox, at least that someone here know some script
however, you could have some 'auto-mount' support in fluxbox using ivman, you won't get a window showing you options like kde's automonter, but, still you'll have devices mounted automatically, not really sure about media CD/DVDs, but shouldn't be a problem with USBs.
If you don't like that option, then, you'll have to depend of a file manager like xfe, pcmanfm or thunar (+thunar-volman), but, hey won't actually won't show up a window like KDE, just will give you easy access with two clicks to mount your devices.
Regards