The 90's had some of my favorite concept cars of all time, and since concept cars from the ninty's are tonight's hot topic, here are my favorites from VW, who churned out a good number of awesome concept cars at the end of the decade.
1997 VW w12. Before it was nicknamed "the Nardo" it was yellow
1999 Bentley Hunaudieres
1999 Bugatti Chiron, the other Bugatti with a W18 engine
1999 Bugatti Veyron, from when it was still cool. It also started with a W18.
2000 Audi Rosemeyer, technically not from the 90's, but I'm going to include it anyway
Bonus! The 1992 Audi Avus Quattro