Mods for video games are as popular as ever. They range in size and scope from patches to fix tiny bugs to entirely new games being made. Heck, you can even use mods to capture machinima.

Now is a good time to get into modding, just like it was in the past.

Popular places to get mods:

Want to see what mods can do? Explore these sites for some mind blowing changes to your favourite games.

Nexus Mods
ModDB
Steam Workshop

My favourite mod is SkyUI because without it Skyrim would have been painful.

Modding tools and tutorials:

Skyrim
Skyrim Creation kit (requires a PC version of Skyrim).
Tutorial playlist on how to use the Creation Kit:

Civ V
You need to have the game on Steam and download the Civ V SDK (under tools in Steam).
This is a basic tutorial on how to get started:

Minecraft

Source
Source is made by Valve. They have tutorials on their site ready for you to explore. Create a Mod and My First Mod.

Cryengine
Cryengine by Crytek is a game engine used in a lot of AAA games. There’s are community of people modding games using the engine: Crytek at ModDB and at the Crytek website.

Rage
Id Software’s Rage Tool Kit links to pdf tutorials at the link.