My list could be slightly warped by nostalgia but here goes..
1) MotoRoader - there's just not much more fun than can be had than a 5 player session of moto roader. Games like this set the turbo apart from the Genesis - which always had the slightly better graphics and we all know it. The Turbo had to rely on fun.
2) Blazing Lazers- Balls to the wall shoot 'em up, plus great music
3) Y's book I & II - when this came out me and my buds could'nt wait to show off the cinematic scenes to our genesis loving buddies. Insanely good music with finger flyin' guitar solos
4) Saphire - Only played this recently on the Emu, but the amount of detail is impressive and well beyond what I thought the PCE was capable of.
5) Ninja Spirit - I remember seeing this got a 10 from one of the reviewers in EGM (paid ad??) - I was stoked at the time and it lived up to the hype
6) Psychosis - Another great shooter with beautiful graphics
7) J.B. harold murder club - Truly original game that that was a blast at the time.
Dungeon Explorer - See MotoRoader
9) R-Type - the reason I bought a slo-mo controller
10) Double Dungeons - Again probably a nostalgia pick, but I remember staying up all night numerous times trying to completely map the gigantic last level (took up like 10 sheets of graph paper)- I can almost still hear the music over and over and over and over again all night long..
Sure I missed plenty - the list is based more on memory of my turbografx owning days rather than what i've played recently using emulation