Palm Pre .... Motorola Karma... Samsung Propel.... Sony-Erickson W760.
All portrait sliders, all phones I enjoyed. Easily my favorite form factor. When my BlackBerry Curve died, I was looking for used phones on Ebay to get me to the end of my contract and all three of them were portrait sliders: The Venue Pro, the Torch, and my Pre I already mentioned and ended up with.
I know it is probably the end of the line for them. Even among the keyboard crowd they were not huge sellers. Landscape or the traditional BlackBerry option seems to be it. Nokia will certainly put out a WP with a keyboard- the world wide customer base they have loves them. But a Portrait slider? No chance. I agree with everyone here: WP manufacturers will probably not roll the dice on a form factor that only a small % of a small audience would want. Makes me bummed.