Here's a page dedicated to some of my favorite tools. The coolest of all has to be my CNC Plasma Cutting Machine. It lets me make flat parts quicker than ever. Next up would be my Chassis Dyno, I've wanted one since the first time I tried to tune an engine on the street.
For something smaller, check out the Bead Form tube beader. I don't know how any custom swap shop can operate without one. It's a very handy thing to have around. Some other favorites are my Mastercool 71475 Hydraulic Flaring Tool and 71500 Hydra-Krimp Hose Crimping Tool.
Thes next two are especially good tools for the Fiero owner. The Motive Products Power Bleeder is the best way to bleed the hydraulic clutch. For filling the cooling system try the Mityvac MV4535 Cooling System AirEvac Kit