There is a Usenet newsgroup devoted to TeX and LaTeX:
comp.text.tex
A FAQ about TeX is available, with searchable index. It is located in the UK, so access from the USA may be slow at times. ("FAQ" means "Frequently Asked Questions")
CTAN is the Comprehensive TeX Archive Network. You can find almost any available macro file, support program, or free TeX system for almost any platform there. There are currently three hosts, one in the UK, one in Germany, and The one linked to above in the USA.
This site can also be accessed through the TeX User Group web page. Look for a link to CTAN.
My involvement with TeX extends to associated programs, including Metafont and Metapost. I currently use TeXLive (a free win32 implementation) as my TeX system of choice, but have worked with emTeX (DOS, OS/2) for years and MiKTeX for a few years after that.
I am working on development of the mfpic package If you are unfamiliar with mfpic, the idea of it is to use TeX commands to write .mf files, then input those to Metafont to create figures. This is accomplished with the aid of a file of Metafont macros called grafbase.mf. I have written grafbase.mp, an alternative, that when input instead of grafbase.mf, allows Metapost to process the .mf files written by mfpic and produce EPS output.
The latest grafbase.mp and versions of mfpic are available for download.
mathdots.sty is a style file equally usable in LaTeX or plainTeX. It "corrects" the definitions of \vdots and \ddots, and adds an "inverse diagonal dots" command, \iddots, just like \ddots but on the opposite diagonal, lower left to upper right. The corrections include making the vertical dimensions scale along with the current math sizes, and taking the "dot" from the same math font as the math punctuation dot rather than the current text font. You can get it here.
mpsproof.tex is a drop-in replacement for mproof.tex which can be used to view proofs of MetaPost figures. mproof.tex is hard-wired to produce proofs only for tex+dvips, whereas mpsproof will do the same, but also allow the use of pdftex. You can get it here.
S Srinivasan Mohan and I have written a terminal driver for gnuplot for producing graphical output in Metapost format. It was included in gnuplot version 3.7. The curent version, shipping with gnuplot 4.0, has had several changes and I have not kept up with it, nor with the current gnuplot terminal interface.