Here are the file types that my version of DefIcons.Prefs will recognize.
I have written down here the xxxxx from the def_xxxxx.info file
eg. the midi file icon will be called def_midi.info, the game icon will be
called def_game.info et.c.

=============================================================================


project
+	ascii
	-	MuFS_KeyFile		Multiuser Filesystem keyfiles
	-	html				hypertext markup language (web pages)
	-	amigaguide			amigaguide documents
	-	doc             	documents*
	-	postscript			postscript print files
	-	fd					?
	-	mountlist			amigados mountlists
	+	filearchive
		-	uuencode		uuencode
	-	install         	ATs installer language script
	+	src
		-	p					pascal source code
		-	c                   c        "     "
		-	cpp					c++      "     "
		-	h					header file for c or c++
		-	i					header file for asembler
		-	asm					assembler source code
		+	basic
			-	bbasic			blitz (or other text basics)
		-	e                   e source code
		-	m					e module
	-	tex					latex document
	-	make                a c (or maybe some other language) makefile
	-	script				amigados script file
    -	email				email messages
	-	prolog				prolog source code
	-	rexx				an arexx script
	+	tool                an executable program!
		-	device				an amigados device	eg. printer.device
		-	library             a run-time library
		-	keymap				a keymap!
		-	font				guess
		-	printer             printer description files
		-	sfx                 LhA self-extracting arcive
		-	filesystem			an amigados filesystem eg. crossdos.filesystem
		-	handler				an amigados hander e.g speak-handler
		-	loadmodule          ? Is it for making resident?


	-	iff						guess!
	+	iff
		+	sound
			-	8SVX			what we usually call IFF sound files
			-	AIFF			not widely used on amiga, maybe on Macs and suchlike
		+	video
			-	ANIM			IFF animations
		+	music
			-	SMUS			Sound of music files
			-	CMUS			??
			-	DMCS			Deluxe Music files
		+	ILBM
			-	brush			iff brushed eg. from dpaint
			+	game
				-	worms		worms levels are special ILBMs
		-	KICK                kickstart files for the 3000?
		+	game
			-	dune2           Dune 2 save games

	-	empty					files which are no bytes in size
	-	object                  linkable object code
	-	lib						link-time library

	+	archive
		-	lharc				good old LhA/lzh
		-	lzx					this is a new archiver
		-	arc					umm guess
		-	arj					umm guess
		-	zip					umm guess
		-	zoo                 zoo is hardly used now.
		-	tar                 tar is mostly for un1x spods
	+	diskarchive
		-	dms				diskmasher
		-	warp            umm, a disk archiver
		-	zoom			umm, don't know
		-	lhwarp			try an easier one!
	+	picture
		-	gif				gif
		-	jpeg			Jpeg pictures
		-	png             portable network graphics (GIF replacement)
		-	reko			klondike deluxe card sets...
		-	bmp             windows/OS2 bitmaps
		-	tiff            guess
		-	sunraster       sunraster!
		-	pcx             pc exchange
		-	targa           targa*
	+	video
		-	quicktime       quicktime movie
		-	fli				fli/flick anim
		-	mpeg            mpeg anim.
		+	riff			some sort of interchange file??
			-	avi         It's just an AVI anim to me mate!
	+ sound
		+	riff            some sort of interchange file? I don't know!
			-	wave		the sound files you get with windows (spit!)
		-	sunau			sunaudio files*
	+ music
		-	med             MED/OctaMed modules
		-   mod				sound/noise/pro tracker
        -	midi			midi files
		-	s3m             Screamtracker (I think they're called this anyway)
	-	kickstart
	+	src
		+	basic
			-	amos		amos source code
			-	amigabasic  guess
			-	gfa-basic	guess

	-	font				usual amiga font
	-	outlinefont         outline font - don't ask me what types
	+	game					} helpful to know what these files are
		-	civilization        } if you delete a saved game by accident
		-	CannonFodder		} you _always_ regret it!
		-   AlienBreed			}
	-   LWOB                Lightwave scenes & objects
	-	WordPerfect			WordPerfect document (V5)
	-	Word 6				Word 6 document (windows)
	-	SpeccyGame			spectrum snapshot
	-	SpeccyScreen		the screens that zx.datatype recognises (from Aminet)
	-   PicView				an image cataloguer
	-	PREF                preferences files



    +	filearchive			}	These are the packers....
		-	powerpacker		}	guess which are which?
		-	imploder		}
		+	xpacker			}
			-	tool						}
			-	amigaguide					}
			+	iff							}
            	+	sound					}
					-	8SVX				}
					-	AIFF				}
				+	video					} These are the things which
					-	anim				} have been packed
				+ music						} and are exactly the same as
					-	smus				} they were above!
					-	cmus				}
					-	dmcs				}
				+	ILBM					}
					-	brush				}
			+	sound						}
				+	riff					}
					-	wav					}
				-	sunau					}
            +	PicView                 PicView V2+ can automatically xpack files
		-	compress					un1x compress
		-	gzip						gzip
	-	library							amiga basic libraries?


=============================================================================
The following are IFF types you may be interested in knowing about...

8SVX	-	Common and garden iff sound file
ACBM	-	AmigaBasic picture
AIFF	-	A kind of Apple Mac sound file
ANIM	-	Anim as saved by dpaint
CAT 	-	('CAT ') Not entirely sure but it's not a .catalog file ;)
CMUS	-	Not exactly sure... some old music format?
CTLG	-	WB2.1+ Catalog files.
DMCS	-	Deluxe Music save files
DTYP	-	Datatype files (the ones you click on to activate the datatype)
FTXT	-	IFF text (as saved to the clipboard etc)
ILBM	-	Your common and garden picture file
ISTG	-	Imagine staging file
LIST	-	Not sure ;)
LWOB	-	Lightwave object
PREF	-	A catch all for iff preferences
RGB8	-	Imagines 'quickrender' files
SCEN	-	Dune 2 (and I believe some other games)
SMUS	-	Sonix save files
SWRT	-	FinalWriter documents
TDDD	-	Turbosilver/Imagine objects
WOWO	-	Wordsworth documents

=============================================================================