Most of the top ones you find are helpful ones like camera controls and such
The IGE can be helpful sometime (though it is the biggest form of cheating ever)
A real world map is also good
I can't even remember all the mods I use
And I still can't get that Hitler Mod to work
Alright, I'm game.
Enter steamid, change "profile" to "card"(or "status"). From there, you can select to use a custom background or the last played game's background. Very useful for tracking the Steam playlog. Alas, I haven't found a similar for thing non-steam games.