I personally use the TDM Modpack Version 1.72. It is a general AI improvement mod that does not add any new technology or components to the game, but does add several races (including my own pet project, the Rage Collective - but that is another story
). I use it specifically because I am trying to make new races that are compatible with anyone's installation.
There are several good mods that do modify technology and/or components that sound great, but I have not used them, myself.
The best place that I know to look for mods is in the Scenario/Mods section of this forum under Space Empires: IV - AI Races/Ship Sets.
I hope this helps.