SimPE, the ultimate tool to edit your Sims 2 characters. You have to have Microsoft's NET Framework installed. Full description here
The Sims 2 Trainer +14, unfortunately it only works without the official Maxis patch installed.
The Sims 2 Trainer +2, it works with the official Maxis patch installed.
TS2Enhancer, you can download the free trial for 48 hours here. I use this program even though it costs $19.95. Well worth it.
Nude censorpatch, without .exe modification. Unzip the file into My Documents\EA Games\The Sims 2\Config folder.
Full description here
UPDATED !! Sims2Pack Clean Installer, version This tool allows you to install Sims2Packs which you downloaded without installing hacks. More here.

Like with anything, even though I've tested all mods and programs
extensively, please BACKUP your neighborhoods before you use any
of the mods and programs. I did too :)