Historical "Touring" Cars (both National and World series) from 60's - 90's. There are so many iconic (road) cars that were taken to the track.
We've raced a Historic road car series for over a year now on GT5, it's incredibily popular with the more mature (in years) players. Everyone is screamiing for more Historic race cars.
Everything from the Mini's, 'scorts, Capri's, Cossie's, M3's, CSL's, 635i's, R31gtrs, TWR Jag XJs, Commodores....yank tanks... AMG 300sl (I think it was the 300sl) etc etc etc - even the old skool Volvo 240's were cool. Then look at the boom of the national series in the 90's using the 2 liter N/A engines and the "world final" of such series.
Totally awesome....oh, but not for GT5.... pffffft - Polyphony, you are really missing a trick here - Historic cars are SO popular on GT5 amongst the older players, sort it out.
Even if it were classic Le Mans / DTM / GT500 - anything, just more Historic racecars - they're awesome