I've always had an interest in unusual and rare vehicles.

Of the honourable mentions, some did run in the North East.

The rear engine Tiger as mentioned was operated by OK Travel for a number of years. They aquired it from Leyland and converted it to single door and operated it until sold to Applebys. It gained fleetnumber 4830. It has ended up in preservation, and I'm sure I've heard somewhere that it's now back in the North East.
Photo - https://flic.kr/p/5cUPLH

Northumbria Motor Services had a Dennis Lancet on long term loan in 1987. It ended up on demo to other operators including Eastern Counties, and it ended up in Wales after it's demo work was completed. I believe it might still be knocking about somewhere (was last with DJ International in Scotland)
Photo - https://flic.kr/p/czqHUQ

MAN NL222. Only one exsists in the UK as N222LFR. There is a good story about this vehicle. Back in 1997, it was on demonstration (It was in fact only the second demo bus I have ever seen, will post about the first one after this) to Coastline and based at Wallsend depot. I nearly ended up getting a ride on it one Sunday after seeing it on the 304. Unfortunatley I only had enough money for the bus that would take me directly home. So I didn't get to have a ride on it, and was only here about a week. It spent some time on demo to other operators, and operated for a few indepents around the UK. Recently it was with Hunter's of Clackmannan in Scotland. However in May I went to their depot to find it to get photos only to be told it was sold to a company in Newcastle. However they didn't say which Newcastle and it has yet to resurface. It remain unique in the UK as MAN decided to use the 18:220 chassis, though that could be a devlopment of the NL222 chassis.
Photo - https://flic.kr/p/dq8tjL

Referring the seeing demos. N222LFR was the 2nd one. The first one I saw was M441CCD which was on loan to Wear Buses and was in use on the 188. (Annoyingly the opposite working to the one I was on). It was in use in full Eastbourne Buses Blue and Cream livery. I did however come accross this vehicle later in it's life with Eastbourne Buses. Although by then it had a Blue Front and in the garish Asda Lime Green and White advert.
Photo - https://flic.kr/p/nxXKbd - A photo of it with Wear Buses has appeared on Flickr and I know Aureolin has seen it.

GAC Citybus. Although it was the Citybus version. Similar GAC Rural Bus was operated by United at Darlington depot for around a year. Spent sometime in an advert for Cummins (Had a L10 engine in). Could have been many more, but GAC went bust.
Photo of the United one - https://flic.kr/p/dD2uTh

Also on the original post, I've decided to mark with a * the ones that I've actually got my own photos of, this includes the honourable mentions.