I often see threads about games, but never anything on mods. A good mod can add months and years to the playability of a game.
Generals: Zero Hour
The Shockwave mod. Don't mind the silly and fairly stereotypical mod name, it is one of THE most balanced, and quality mods I have ever seen. It is higher quality than most expansion packs. It is currently at version .93, and the next version will be .95, and three complete generals will be added.
Renders of new units
Red Alert 2: Yuri's revenge
The cannis rules mod. Most mods for RA2 are simply pitiful, they tend throw a bunch of poorly modeled voxels together, and add unbalanced stats. This mod is focused on making the units you already have more balanced, and only adds a special unit for each country if you select a certain mode.
Very enjoyable.