All of the models you find on these sites are free and of no charge. And of very high quality.
http://www.pdf995.com/download.html (here you can download the PDF software to create you own)
http://www.tamasoft.co.jp/pepakura-en/download/viewer.html (this is the pepekura unfolding program for the 3D models)
http://www.metaseq.net/english/index.html (here you can download the 3D modeling software)
http://www.photofiltre.com/ (here you can download the phot software I use just click english then go to downloads)
http://www.cardmodels.net (this is the zealot hobby fourm just click and become a member lots of models and tutorials)
http://405th.com/forums/index.php (here there is lots of paper armour from halo)
http://compositecreationsltd.com (Models and fonts as well as a very good plastic version of the USS Sinclair)
http://www.homespunmagixx.com/ ( a few star trek models)
http://jleslie48.com/ (lots of sci-fi models)
http://web.mac.com/michaelhaggard/ALBIONRISING/Welcome.html (doctor whos' tardis and a few star trek TOS props)
http://www.3dpapermodel.com.tw/ (vast archive containing a few star trek models)
http://aliens.humlak.cz/aliens/aliens_papirove_modely_gb.htm (ALIEN paper models and a starbase and terminator models)
http://www.freewebs.com/jaybats/dealerschoice.htm (lots of star trek and stargate models that are simple to build)
http://www.d1.dion.ne.jp/~hamanaga/ThumbLink/Thumb453.html (large collection of sci-fi models)
http://www7a.biglobe.ne.jp/~sf-papercraft/ (star wars and star trek and the time traveling delorean)
http://cleversantoro.spaces.live.com/default.aspx (star trek ships and more in production)
http://community.webshots.com/user/missouri1981 (some good star trek models)
http://www.freewebs.com/paragon19/ (star trek and planes avalible here)
http://skipspepakuracostumes.blogspot.com/ (blog showing progres of various armours)
http://www.geocities.jp/ikenohata2005/papermodel2-e.html ( japanes site some good but complicated models)
http://paperinside.com/ ( lots of very good models especially bumblebee)
http://www.paper-aviation.de/ (some star trek and various other models)
http://www.freewebs.com/yankee44/freepapercrafts.htm (very good star trek and stargate models)
http://www.newmoonprops.com/ (brilliant site lots of props and very low cost)
http://www.roddenberry.com/ (the official roddenberry online store)
http://www.lcarscom.net/databank.htm (genreal star trek know-how)
http://www.lcars-interface.de/ (lots of downloadable LCARS screens)
http://www.cygnus-x1.net/links/lcars/ (lots of blueprints of star trek ships)
http://www.trekprops.de/ (tutorial on how to make your own PADD out of styrene)
http://www.lcars.org.uk/index.html (lots of information on the LCARS OS)
http://www.mattmunson.com/props/ (nice showcase aswell as prop tutorials on how to make your own)