C

@rikdatta 

A lot of the games have been upgraded with community-created unofficial patches that fix a lot of their bugs and compatibility problems. You can find them here:

Command & Conquer 1:

• Nyerguds' C&C95 v1.06c revision 3 patch (which also adds bonus missions originally exclusive to the Playstation and Nintendo 64 versions of the game)
  Note that this patch fixes two quite common and completely fatal game crashes (top-of-map reconnaissance crash, stealth crash), so installing it is strongly advised.
• HD music pack, with stereo music for the game.

Red Alert 1:

• Funkyfr3sh's automatic Red Alert 1 patcher/installer (The thread also has briefing videos for the expansion missions, converted from the Playstation version of the game)
• Nyerguds' main.mix cleanup for TFD/TUC (Not really needed, but cleans up about a gigabyte of unnecessary files in the RA1 folder. Unpack in the game folder, run "patch_main.bat", let it finish, and then delete the files you extracted.)
• HD music pack, with stereo music for the game.

Tiberian Sun:

• Funkyfr3sh's Tiberian Sun patch

Red Alert 2:

• I advise installing the CnCNet online play installer for RA2/YR. Even if you're not interested in online play, it comes with a bunch of automatic fixes. It should automatically take care of the "black screen on startup" issue, and has a configuration tool that allows further tweaking of the game's settings.

Generals:

• GenTool seems to be the main patch for Generals these days. The website is kind of vague on what it does besides restoring multiplayer and adding anti-cheat, but I heard it does a lot to make it work better on modern OSes too.
• If you have issues with DirectX errors popping up, find and delete the file "dbghelp.dll" in the game's install folder.

Renegade:

• The Tiberian Technologies patch fixes loads of issues on Renegade.