Command & Conquer Tiberian Sun.

@Tommerz87 

Note that the oldest three games (C&C1, RA1 and TS) are all freeware.

Anyway, that aside, since you already got the pack on the EA App... 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:

• GenPatcher seems to be the main patch for Generals these days. It's a complete solution that fixes every known issue in the game.

Renegade:

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