I don't know how many 3-rail Scalers visit the 2-rail side of the forum, so I thought I'd post this here about Union Station Products offering O-scale versions of their passenger car sides:
http://unionstationproducts.com/_9004.html
And if we add parts from Delta Models:
http://www.deltamodelsusa.com/
we almost have the makings for some nice passenger cars.
Trucks are needed, as well as car ends and roofs, but from what what said on the 2-rail side one of these makers may start offering ends and roofs too.
Anyway, FYI.