Links

General 

3D Upright Sinistar model
3D Cockpit Sinistar model
Sinistar.com - good information. 
Evolution of Sinistar
King's Sinistar Index
KLOV - Sinistar 
Eddie's Arcade Shack Sinistar

Purchase 
Buy Williams Arcade Classics at GT Store - do a search on sinistar 
(* Williams Arcade Classics is DISCONTINUED as of sometime around 7/99)
There are a few games sites that are still selling the CD, so you may be able get one before supplies run out.  I just found a copy at Got Software?

Repair parts
Joystick handle - New machined replacement with red ball $19 (Search page for Sinistar)

Conversion 
Joystick Hack
Williams Conversion FAQ
Sinistar Schematics
Sinistar Manual
Sean Riddle's Williams information
Nick's Williams Multi-game hack