I am 99% sure a R8 Spyder or a Ferrari would be in my stable otherwise......
P.S. I went back through and read some of the replies in this thread and thought I'd add my 2 cents, a few of the cars mentioned such as the e46 m3, 997, GTR, e92 m3, s2000, etc are all nice cars in their own category but certainly not a competitor to the NSX by any means. Closest may be the s2000 but I've owned over a dozen s2000's of every year and color, they will never be an NSX!
I loved my e46 m3, it's a true epic car from BMW and probably the last true M-car IMO, the e92 m3 is nice but too luxurious and a fat pig to be considered a driver's car. I DD a e90 m3 with two baby seats, it's ok to cruise but definitely not the car I would grab the keys to if I was going out by myself for a drive nor do I consider it a driver's sports car.
GTR is another fat pig, I don't care how fast that car is, with the auto tranny it's so boring to drive. I don't want to offend GTR owners but even many owners admit to me that the car is so fast but boring since it's the car doing the driving not the person.
I think the 997 GT3 is the "closest" competitor to the NSX in 9/10 aspects. This is how good I rate the NSX in terms of an overall fun car. I know it will never beat a GT3 on the track but it's probably the most fun you can have legally on 4-wheels without spending silly money (anything over $150k).
My s2000's are fun cars and would usually be my first choice for going out for a nice fun drive. Least maintenance, most bang for your buck, and if you are driving my supercharged s2k, it's probably capable of keeping up with most stock NSX's
Would love to hear other people's opinions on this too so chime in!