I'll start by saying good thread, this could bring some good replies in! i could go on with a list as long as my arm, i cant remember anywhere near all of them.
saw a morgan 3 wheeler today actually which was interesting, gt3 rs 4.0 a little while ago, ferrari f40 and f50 AND enzo in my home town, mclaren f1 gtr-possibly the best looking machine ive ever seen, jaguar xj220, audi rs2, e30 m3, an orange zonda f, mk2 (remake of the 1965 version) shelby daytona coupe, ahh ill have to stop, ill add more as i remember, its hard to rattle them off in an instant. never seen a veyron, very irritating as i worked for a guy whos best mate has owned 3, amongst other beautiful motors.
I made a last-minute decision to try to hook up with the West Yorkshire contingent of the TVR club for their "Cobweb Run" this morning but I was a few minutes too late. Shame, because that would have been a lovely collection of rare and very noisy cars. I saw the Cerbera Speed 12 running-in after a re-build at Sherburn Aerodrome near Leeds last summer. Awesome.
I saw a 458 Italia last week and I've seen an F40 and an F50 on the road. You see a few Porsches but nothing as exotic as a GT3 RS 4.0. I'm up in West Yorkshire wheer exotic cars are a bit thin on t'ground, tha knaws, but my youngest son is at the end of his 3 years at uni in Hampshire and sees a lot of lovely, exotic cars on the road.
Being near to London I have seen cars of all kinds, new exotics to pristine cossies and classic astons. mp4 12c is a beaut, speed 12 is way up there - good spot. West London during the summer is the place for exotics, most on middle eastern number plates.
Apart from an F40 in Henley on Saturday there hasn't been much recently. A Testarossa in the Henley area early this year, Aventador on the A4 near Reading late last year as well as a GT3 RS 4.0 on the M25. A few years ago I followed a bright green Mosler MT900 into Salisbury. A tough thing to do in a 205TD!
Thruxton used to have a Murcielago 670-4 SV last year and then got rid of that for an Aventador. The buggers.
A guy in the south Wilts area has (or at least did have) an original single seater Bugatti thing. One of those oval grilled things painted bright blue. Sounded incredible and he didn't hang around. (It broke down on him one day and a few of my very good friends were around to give him a hand, which is how I found out it is original).
About 15 years ago I saw a Nissan R390 on the road. Will never ever forget that, think it's one of only 2?
Edit: 2 years ago I also saw the only Brabus Unimog on the M3 getting onto the M25.
An r390 is pretty special! I once followed an original (or at least I thought original) gt40, all the way to it's house, it was an average Joe housing estate, and a lad I went to school come to the front door to greet his dad home... I asked him if it was real, it was a replica took the jam out of my donut for sure.
A couple of SLR's around Epping and McDonalds at stansted, and the SLR 722 (if anyone remembers that one) on the a406.
Had a spirited drive with a Ferrari 458 Italia some time ago. I know its prob not the rarest of cars but here in Wales it is!haha. Amazing sound and he was pushing it!
Also a Merc with a racing body kit (like Le Mans or something) went past me at about 150+mph a while back. Saw it coming from about 1/4 mile away and knew it was moving, then it went past and was gone in like 2 seconds!