For some people, myself included, "Very Slow" research times just aren't quite slow enough. Particularly if you like long, drawn-out games on Gigantic and Immense galaxies.
The solution is simple, but tedious. Go through all the tech trees and manually increase the cost of each and every tech in the game. Well, I really don't have the patience to do that, so I came up with an easier way.
Open up TechTree.xml with a text editor (i.e. Notepad). You'll find it in the GalCiv2\Twilight\Data\English directory for Twilight, GalCiv2\DarkAvatar\Data\English for Dark Avatar, or GalCiv2\Data\English for Dread Lords.
First thing you need to do is save a backup copy, for when you want to go back to normal research speeds.
Now, open up the editor's Replace tool, and replace every instance of "</Cost" with "0</Cost" And that's it. With a single mouse click, you've increased all the research costs tenfold. For Twilight of the Arnor, you'll also need to do this in each race's individual tech tree file. Again, remember to save backups.
For comparison's sake, I recorded the different research times for Terrans' Artificial Gravity at the very beginning. I used a Large map with common everything.
Very Fast: 5
Very Slow: 22
Very Fast: 52
Very Slow: 225