List of mods available here

Non-Cavedog 3.1 Patch
TA Recorder and Hook
TA BugFix by Switeck
TA:Mutation
The Lost Legacy's Race
UberHack 4.0 with its own switching program
UberHack 4.0 for TA:M
X TA version 0.95

Community Pack
Tech Level4

A brief explanation of the files:

        The patch is necessary for good game play.  It is the PC version.  Install Total Annhilation, the Core Contingency(if you have it) then Battle Tactics (if you have it) then the patch.  If you don't have Core Contingency, then you will see units you might not be able to use, and will therefore be greyed out.  

        TA recorder records your games.  It also has a utility in it that will make building lines of buildings really easy.  I'd getting it, because it is necessary for internet play.

        TA BugFix fixes things that Switeck believes to be bugs in TA.  It also does a little balancing.  For a explanation of what it changes, read either the short or long version.

        TA:Mutation is a program that manages your mods, units, and maps.  It isn't necessary, but it comes highly recommended.

        The Lost Legacy's race is ok, but I felt like it was too powerful.

        Uber Hack is my favorite mod.  Occassionally you can play online with someone.  It comes with a tough cheating AI.  

        X TA is a mod made by The Swedish Yank Spankers.  I haven't played it, but since they made the recorder, I assume its pretty good.