[Captain Joy]

• GURPS Basic Set is necessary, unless you're minimizing costs and going pure GURPS Prime Directive.
• GURPS Prime Directive was a good starting point for templates and what-not, but now I almost never reference it.
• GURPS Space is useful for star system and planet generation, and the occasional rule for dealing with different gravities and atmospheres.
• GURPS Spaceships combat rules are good for giving every body something to do during a ship battle, but I've never used it to build ships.
• GURPS Psionics Powers is indispensable if psionics will be a part of your campaign.
• GURPS Ultra Tech is useful, as it is in any ultra tech setting.
• my GURPS Star Trek webpage is amazing and should be used by anybody running an original series Star Trek campaign, but I may be biased.