This section collects my favourite links. The list is not ordered by importance. The main criteria I'll follow is the contribution to my DIY projects. This is only a part of my bookmars file . Actually this file contains  several hundreds of links

DISCUSSION GROUPS WORTH A VISIT
  Full Range Driver Forum :
 www.f18.parsimony.net/forum31999/
  Very intersting  is also the single drive website :  http://melhuish.org/audio/index.htm

Another big source of infos about SETs and Flea power sistem is Audioasylum:
 http://www.audioAsylum.com/

For lowther fanatics:
 http://www.egroups.com/group/lowther

DIY TUBE TOOLS
  http://www.pi.infn.it/~federico/unofficial.htm
Federico Paoletti's homepage. In the section "Futher projects" you can find a very interesting "computerized vacuum-tube curve tracer".  Very nice is also the "vivisection" of the  Audio Analogue PAGANINI CD player.
 
http://members.aol.com/sbench101/
Steve bench's pages are the best if you look to instrumentation projects, or data about the comparison of tube preformaces and different topologies. Please take a look to them before startin any project.
 

 
TUBE & MATHs

http://web.tiscalinet.it/teodorom/index.htm
Not for the faintharted: Teodoro Marinucci's homepages. All the formulas you need and much more (unfortunately only in italian). 

 http://web.mit.edu/cheever/www/main.htm
Basic Formulas. Nice thesis.

 http://www.winternet.com/~biro/articles/
Tube parameters identification using computerized methods.
 

DIY TUBE AMPS/ DATA SHEETS
   http://www.svetlana.com/docs/TechBulletins/TB.html
Of course the strarting point for details on Svetlana tubes. Expecially this Technical bulletin section is full of information about these high performace tubes. I have a dream: to visit the factory but this seem impossible... for now  ;)

Other informatin on DIY russian tube project can be found at:

http://www.duncanamps.com/
Ducan's site contain lot of information on tubes. The tube search engine is very nice and can be a starting point to get information and link to tubes  In Ducan's site you can find a group of interesting links to other modelling/datasheets  sites.
Among them i'll mention:
http://www.ccinet.com/~phineasgage/
Matts tube Page, one of the biggest, full of project an data sheets:
http://www.vt52.com
VT52 Homepage, nice to navigate and with very interesting line/louspeakers project.
http://www.phy.ohiou.edu/~cigna/tubes/
David Cigna's Homepage. Here  you can find  very simple models and a lot of data sheets.

http://www.aston.ac.uk/~saddrj/siteinde.htm
Russ Sadd site is worth a visit. Lots  of information about almost all the subjects  that matter in DIY tube circuits.

http://web.mit.edu/cheever/www/main.htm
Dan Cheever site is lot of information regarding biasing tubes and about distortion modelling. Unfortunately the site is no longer mantained

http://www.geocities.com/ResearchTriangle/8231/
Andrea's site has a large display of DHT project  and many information on other subjects such as electroststat, DIY D/A converters etc.

http://www.geocities.com/CapeCanaveral/4573/
Cesare Lavazza's homepage has lot of proyects, several of them regarding  DIY DHT amplifiers.
Besides there are lot of interesting details on Power supply building.

http://www5.big.or.jp/~dh/  Direct Heating s is of course the best site to grasp the basic philosopy of DIY  DHT amplifiers. Unfortunately   now Sakuma is in triode Heaven
 

 http://space.tin.it/scienza/stperu/PAE.htm
Perugini's page devoted to Tube DACs & specialty Tubes 

DIY PLASMA TWEETERS

Thank to the very useful advices of Ulrich Haumann, I've build a plasma tweeter. This is an incredible experience. The tweeter has one of the best highs I've ever heard. Thank you Hulrich. Some day I'll add some photo of the prototipe on my site. Unfortunately this tweeter has very low efficency.

http://members.aol.com/uhaumann/eplasma.htm This is absolutely the best starting point. As far as I can see his site is the ONLY ONE on internet to give detalis to build a very simple and working plasma tweeter

http://sundial.sundial.net/~rogerr/ionovac.htm this site has historical details on plasma tweeters.

http://uts.cc.utexas.edu/~speakers/audio_designs/designs.html
This site is the best if you want a quick start. There you can learn of to rapidly build a very simple loudspeaker. I've started from here.

http://www.clarkson.edu/~stokessd/quad.html
Stoke's page has a lot of details on Quad and working theory of electrostats. Besides you can find nice informations and projects on DACs and Tube Amplifiers.

Two  for All.. HI-FI audio pages... Please take a look at the wall clock from time to time.... you run the risk of spending a lot of time there... ;)