This was taken from a post I made elsewhere //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif
http://www.zaphaudio.com/ - John Krutke's excellent site, concentration on smallish 'bookshelf' monitors and component comparisons
http://www.frugel-horn.com - full range, single driver, crossoverless designs
http://www.speakerbuilder.net/ - a good mix of bookshelf and floorstanding speakers, easy-to-obtain parts
http://www.humblehomemadehifi.com/ - very wide variety of tested speaker designs, from the economical to the no-holds-barred high end
http://www.partsexpress.com/projectshowcase/homeaudio.cfm - the PE project showcase. Lots of different ideas to try out
http://t-linespeakers.org/projects/index.html - transmission line speakers and subwoofer plans
http://www.quarter-wave.com/Projects.html - Martin King's quarter-wave speaker projects section, excellent information if you're thinking about building a tuned quarter wave pipe of any kind.
http://www.zillaspeak.com/bib.asp - probably the simplest-to-build horn plan out there, a good single driver, no-crossover solution. The companion thread on DIYAudio is here:
http://www.diyaudio.com/forums/showthread.php?threadid=66173
http://members.myactv.net/~je2a3/open.htm - JE Labs open baffle plans. If you're curious about getting openly baffled, might be a good place to start looking
http://passdiy.com/speakers.htm - Nelson Pass' superb DIY section. Small speakers, BIG cabinets. Big fun.
http://www.quadesl.com/tidytl.html - compact transmission line plans for the highly-regarded Jordan JX92 full range speaker
http://planet10-hifi.com/boxes.html - Planet10's box plan library. Related to the frugel-horn project, this is *the* place to start looking if you're thinking about CSS FR125 4.5's, Fostex or other single speaker ideas.