These are all bookmarks to particular stops on mbtainfo.com. This is the best site I've used, though there are still things I don't like about it. The main thing I don't like is that the page takes multiple round trips to load something that could be just a simple lightweight page of html with inline css, and occasionally I have poor cell service when I'm making one of these requests.

I felt kind of silly writing that. Why have I been using something for years if it's relatively simple and doesn't work how I want it to? So I wrote my own: jefftk.com/nextbus/mbta/. It's very simple, just a thin wrapper around the nextbus API (pdf) to switch it from xml to ugly-but-mostly-mobile-friendly html.

(It's not actually restricted to the MBTA; see the full agency list.)