Right, the aim of this thread is to see what vehicle types that members would have liked to have travelled on but no longer exist or you just haven't been on one in service yet. The only thing is, you mustn't have travelled on that vehicle type before and must be available in UK and Ireland. You are allowed to include vehicles that you have been onboard but didn't move at the time you were on it.

For mine, I am including linking pictures from Flickr as it includes some rare vehicles, I do have photos of some that are on my list but I cannot be bothered to upload them.

1 - Iveco Turbocity 100
One built, and sadly no longer around. If I had won the lottery years ago, this would have been on the list of vehicles that I would have preserved.
Photo - https://flic.kr/p/ccsGNS

2 - Iveco Turbocity 50*
Handful Built. Either all gone or one hiding somewhere.
Photo - https://flic.kr/p/auXAWM

3 - Ace Cougar
2 Built. One Preserved. The other (bodied by Willowbrook) was exported to Ireland and later scrapped.
Photo - https://flic.kr/p/auXAWM

4 - Dennis Domino
Think there is 2 in preservation. One of each body example. The Northern Counties one is restored.
Photo - https://flic.kr/p/8R4rry

5 - Iveco EuroRider / Marshall Maxi*
3 Built. 2 as Ambulance and one as a demo bus which ended up with Whitelaws. I've got photos of it, but here is one taken by Matthew Edwards on the same day that I took one.
Photo - https://flic.kr/p/oFJMbF

6 - Optare Citypacer*
Although I have a few photos including those converted to motorhomes. I've never travelled on one.
Photo - https://flic.kr/p/6WAzte

7 - GAC Citybus (KC Class)
There is one of these preserved along with one of the Double Deckers. Whilst the Double Decker KD Class had Detroit engines in. These had a similar drive line to the B&C reg Olympians of Go-Ahead Northern. They had the Cummins L10 engine, but coupled up to a Voith 3 Speed Box - Here is a video of one too - https://www.youtube.com/watch?v=UDKH_gYSO_U
Photo - https://flic.kr/p/kArm8e

8 - Quest Range of Single Deckers
Quest built a number of odd vehicles. Usually with a chain driven engine. Here are 2 that I particularly would have liked to sample. The A-Reg one was used around Heathrow Airport and was last reported as a motor home, whilst the Blue and Cream C-Reg one is preserved and appeared at a Showbus 2008 which I didn't attend mainly due to having a bit of a depression at the time and wasn't really interesting in going to rallies. The vehicle has disappeared off the rally scene and is believed to be parked up in a corner of a yard somewhere.
Photo - A Reg Quest - https://flic.kr/p/aSuzwK
Photo - C Reg Quest - https://flic.kr/p/5qgfVq

9 - MCW Metropolitan*
Always wanted to get on these. Although Tyne and Wear PTE had the 2nd largest fleet of them. Nearly all of them were gone by the time I was 6 years old. A handful survive in Preservation including a T&W one which when finished with be a credit to the owners of it.
Photo - https://flic.kr/p/dGhw5r

10 - Bedford JJL*
One of the most Attractive Minibuses I've ever seen. Only one survives as a Motorhome now which I have seen in the metal. Only 4 of them built all with this attractive bodywork by Marshall. Then General Motors pulled the plug on Bedford and then they were no more. The sole survivor has since been painted yellow as seen in the photo. It was still white when I saw it last time.
Photo - https://flic.kr/p/ozasUS

Honourable Mentions - Those that didn't quite make the top 10.
Dennis Falcon V Double Decker
Dennis Dominator Trolleybus*
Dennis Lancet*
Leyland B21*
Leyland-DAB Bendy Bus
Leyland Tiger (Rear Engined)* AKA Q723GHG which ran with OK Travel.
MAN NL222
MAN 18:240 LionCity DD / ELC Kinetic+*
MAN SG192
Neoplan N416
Neoplan N4009*
Scania K92 Double Decker*
Volvo B57
Ward Dalesman GRXI

Will be interesting to see the views of other members.