There were several titles that had separate PC and PCjr. or separate PC and Tandy releases. In this post, I will identify many of the more desirable games that are known or suspected have a Tandy or PCjr. version that displays superior graphics, sound or both. You won't find these games in any DOS or ROM collection, on any abandonware site, from any torrent site, or to buy from any legitimate retro PC game selling site like Good Old Games. Where I know of corroboration for these games, I will give it.
Action Fighter - Tandy
http://www.pixelships.com/adg/epf006.html - Supports 16-color 320x200 graphics and 3-voice sound. Only EGA and CGA versions widely available.
Agent USA - Tandy
Supports PCjr. graphics and was advertised for sale in Tandy's catalogs, so a Tandy version with support for enhanced graphics may exist.
The Black Cauldron - Tandy & PCjr.
Retrograde Station released cracked versions of the booter version of this game. The versions they released were v1.1J, v1.1K, v1.1K Tandy and v1.1m. None will not work on either a Tandy or PCjr. with the exception of v1.1m. The DOS-installable AGI2 and AGI3 versions of this game will run just fine on these systems.
Gauntlet II - Tandy
Gauntlet II had a bonus disk, which you had to send away for to Mindscape, that added digitized sound support for owners of a Tandy 1000 with a DAC, such as the TL, SL and their successors.
The Seven Cities of Gold - PCjr.& Tandy
Retrograde Station's disk 2, containing the map editor, is broken. I also believe that disk 1 may be corrupt in a less obvious way as well. Despite displaying Tandy 1000 support on the box and being sold in Radio Shack, the CGA version is used for Tandys with the RS booter. On real disks a custom 4-color palette is used for the Tandy. Only the PCjr. version supports 3-voice sound.
Styx - PCjr.
http://www.mobygames.com/game/styx/cover-art - Styx came in a version for the PCjr., and while it looks identical to the PC version, it supports 3-voice sound.
Superbowl Sunday - Tandy
Supports enhanced PCjr. graphics. Advertised in Tandy's catalogs, so a version that supports enhanced graphics on a Tandy may exist.