For me the following Race-Cars are major fun too:
S2000 LM Race Car
Integra Type-R RM
Integra Type-R Touring Car
S800 Race Car
Cappucino RM
Elise ´96/-111R RM
Clio Trophy Car (Lutecia or Renault)
FTO Super touring Car
Falken GTR R34
BMW 320i WTCC Touring Car
JGTC/Super GT/ GT300 All are superb (stock or tuned)
DTM Cars (and those PD legalised for this categorie: M3GTR and the R8 LMS)
All have good Handling and do what you want
But the ALFA TZ2 is an other Category (for me) its so good and easy to drive
The stock Elise 96' rm on racing softs is great to beat supercars. The Classic
Race cars are a blast to drive especially the 69 camaro rm and Ferrari p4 330 without abs.
To add to my previous comment, the race cars I've found to enjoy the most is the Peugeot 905 and the Bentley speed 8. There both so nice to drive, turn in is very nice, hitting apex's is easy, its just a great experience and easy to ace a lap
Are you asking for only racing spec cars?
If so, then in my opinion from my own collection of exactly 300 cars:
PAlfa Romeo GIULIA TZ2 carrozzata de ZAGATO CN.AR750106 '65 PMazda 787B Race car '91 PLexus IS F RM '07 PTVR Tuscan Speed 6 RM '00 PAEM S2000 PJaguar XJ13 Race Car '66 PRE Amemiya Amemiya AsparaDrink RX7 '06 PSuzuki Cappuccino (EA21R) RM '95 PPagani Zonda R '09 PAmuse S2000 GT1 Turbo PChevrolet Camaro SS RM '10 SSpoon FIT Race Car '03 SHonda NSX-R Prototype LM Road Car SLamborghini NOMAD Diablo GT-1 '00 SBMW M3 GTR Race Car '01 SMazda Furai Concept '08 SVolkswagen Lupo Cup Car '00 SHonda MUGEN MOTUL CIVIC Si Race Car '87 SShelby GT350R '65 SFord GT40 Race Car '69 SHonda S800 RSC Race Car '68 SChevrolet Corvette Z06 (C2) Race Car '63
Or, if you just want fun cars to drive in general:
P stock Ferrari 458 Italia '09 P stock Corvette ZR1 (C6) '09 PMazda Roadster RS (NC) '07 tuned to 206 hp, 931 kg, 433 PP with Racing Mediums PMazda Eunos Roadster (NA Special Package) '89 tuned to 145 hp, 831 kg, 403 PP with Racing Hards PSpoon Spoon CR-Z P Nissan GT-R '07 tuned to 2012 Nissan GT-R specs PBMW 135i Coupe '07 tuned to 2011/12 BMW 1 Series M Coupe specs PLotus Evora '09 tuned to Lotus Evora S specs P stock McLaren F1 '94 PDodge Challenger SRT8 '08 tuned to 2012 Dodge Challenger SRT8 specs P stock Lamborghini Miura P400 Bertone Prototype CN.0706 '67 P fully tuned Fiat 500 F '68 S fully tuned Isuzu PIAZZA XE '81 This car is absolutely a blast to drive. I don't know if it's my tune or what, but I love it. S fully tuned Triumph Spitfire 1500 '74 S fully tuned Ginetta G4 '64 S stock TVR V8S '91 S fully tuned Suzuki GSX-R/4 Concept '01 S fully tuned Caterham Seven Fireblade '02
It's a shame that I spent so much time on that list for it to probably not be used.