As Bradman mentioned Showtime, HD Net Movies, and I believe Sony Movie Channel , Encore/Starz tend to respect OAR if they have access to an HD print that uses it (sometimes they can only get cropped or Pan & Scan copies).
HBO and Cinemax prefer to crop everything to 16:9. According to an article I read a while back though if a filmmaker/studio fights them hard enough about it they will relent and show it in OAR. For the most part though I wouldn't plan on seeing much in OAR on those channels.
I haven't used it a lot, but I believe most PPV stuff on DirecTV respects OAR as well.
As far as something that you could search for and use to set up recordings I doubt it. Tribune who does the guide listings has a bad enough time doing what they do now, I could only imagine how bad they would screw stuff up if they tried listing aspect ratios for the movies.