OK, here are some utilities I'd say you MUST get - or at least give a try. These are the best I've found after much experimentation:
ABCdir - totally awesome (surprisingly underrated) file manager
Visual Prefs - for customizing total look of Workbench
LoadCMAP - to lock the WB palette so it doesn't stupidly change
DrivePrefs - stop that annoying drive click
ModePro - to promote & modify screens
SimpleFind 3 - the best file finder
DiskSalv 4 - the good disk salvage / undelete tool (hard to find)
Scout - the ultimate system monitor (get ver. 37.249)
Hex - old but good binary editor
ScreenShell - full screen shell (make a double height autoscroll screen with ModePro!)
MuchMore - super smooth scrolling text viewer
Fjpeg - fast jpeg viewer
Visage - nice, fast multi-format image viewer
v41sound.datatype - very nice sound datatype
NISClock - best title clock
PowerSnap - clip text anywhere (almost)
Voodoo-X & xadmaster - extract almost any archive
Zoom - nifty little magnifyer that works on any screen
... and there are lots more like TitleShadow, WindowToFront, Iconify, MFR, VersionWB, DoIcon, RunFromWB, Clip, ASLtoRT.