One of the great aspects of Starsiege Tribes is the ability to customize. Since Tribes is written in C++, many people have been able to make use of the code. I personally use the following scripts:

My Scripts

Easy Deploy - My first (and only) client side script. Based off of Mannkind's Beacon Addons, this script helps a lot when deploying items (including beacons). This will automatically move you into the correct position for deploying, so you don't have to worry about correct positioning. Want to deploy a turret? Just press P and it will aim down to the right spot for you!
Requires Presto Pack
To install put this in your /tribes/config/Presto directory and then go up a directory and open the file called autoexec.cs and in that put the line:
Include("Presto\\easydeploy.cs");
Somewhere after the line exec("presto\\Install.cs");

Other Scripts

Presto Pack - A bunch of neat stuff, visit his site...
CmdHUD - Make inventory and command screen overlays, and not new screens. Now you can still see the action
Middle Mouse Repair - Pressing button uses pack, and if it is a repair pack, it switches back to weapon when repair finishes.
Custom Weapons - Rebinds keys 0-9 to allow one finger to change to all weapons by double pressing a key.
An extended menu to allow all of the hidden sounds to be used, including sounds forgotten by Presto's menu (and found by me!)
A change of zoom key and crouch key to become toggle switches.
Short code to always jump before jetting, thus maximizing height and speed.
And a few others...

Download them!