What hard to find stuff do you look for?

[tomustang]

Now we all know our hobby doesn't really have big runs of certain trains, rolling stock, structures or perhaps an older model that's been fading away. Do you have a list of items you're always on the look out for, and yes I mean at a decent price, since I've seen rarer items go for ridiculous prices. Post it up!

Two I'm usually looking for are:

Kato HO SD80MAC
Busch Pennsylvania State Police Car