CLEO The Compact Library Extension Organizer, lets you bundle up all those extensions you have into a single extension, so you can re-install it lickety-split.
As someone says on the page to, they use it so basically they can have different profiles with different extensions in each – nice idea.
Anyway it’ll save that inevitable ‘What the hell was that extension called?’ moment if you ever have to migrate to a new PC!
A close second is ListZilla which creates an HTML page style catalogue of all the extensions you have installed, so you can save it away somewhere in case the inevitable crash happens!