Having always been into most forms of transport, I started to collect them when decent qualit models became available. The main companies that produce them are EFE (Exlusive First Editions), Corgi and CMNL (Creative Master Northcord Ltd). I bought the first ever EFE releases when they were released (or at least when they almost sold out) these were a couple of coaches. I am not sure of their value but they are still mint in box (how I try to keep all my buses). These are in 1:76 scale (which fits in with OO scale model railways, as a comparison HO is 1:87).
One particular interest is in Asian (mostly Hong King buses). Here is a picture of one of my more recent purchases. The picture is from the Oriental Model Buses Website (a lot of model bus photos there).
http://www.orientalmodelbuses.co.uk/...kbus1006m2.jpg
And for something a little different a Japanese bus I bought last year. Photo again from the same website.
http://www.orientalmodelbuses.co.uk/Isuzu/jb5002m2.jpg