Worf's Star Trek page: Not really about Worf, but well thought-out fanpage with lots of goodies.
The Log Book -- excellent episode guide to all Star Trek versions as well as Animateds, and Movies -- plus other TV SF (The Prisoner, Dr. Who, Xena, Red Dwarf, etc.
Paramount's official site, the Star Trek Continuum. Where else could you buy a 7 of 9 watch? Or a Gorn action figure for around $100? All sorts of interesting goodies; emphasis is mainly on current incarnations of Trek..., but there's enough on all Trek versions to interest any fan.
The Sci-Fi Channel's Episode Guide. The Sci-Fi Channel is currently airing TOS; this is an excellent guide to the plots, original air dates, photos, trivia questions, etc.
Creation Conventions. They're the best of the professionally-run conventions. Site includes Trek, SF, Xena & Hercules conventions
There are thousands upon thousands of other Trek websites and newsgroups. You can locate video, music, artwork, screensavers, software, wallpaper,merchandise, autographs, role playing games, computer games, books,articles, timelines, reviews, fan fiction, and even Star Trek search engines devoted exclusively to locating more Trek sites