Be sure to post the tools you use in the comments
Windows Tools
LS1 Flash Tool - Still in development, but you can tell it has a future here.

TunerPro - Has ability to tune and scan, a must have.

WinOLS - Great program, hex editor, has a 2D and 3D view, and more. Great for locating maps in a binary.

HxD Hex Editor - Hex editor.

wOBD - This is a great tool, sadly last update is from 2006. Still a great app, say you want to poll every pid at $22, $3C? This is it.

IDA - Disassembler and debugger.

DISMOT68 - Two pass Motorola 6833X disassembler. Support definition files and structure.
STNTerm - Terminal for ELM and STN.
OS X Tools
Synalyze It! - It's the best hex editor I've used. You can make configs called grammar, highlight bytes, label them and a ton more. Make sure to try the grammar that is provided with the program, pretty neat stuff. Here's a bin I just started working on...

CoolTerm - Well this one is cross platform but only tried OSX version. It has support for AppleScripts, and works great.

Wine - It lets you run Windows programs on OSX.

Linux Tools