This app was mentioned in 2 comments, with an average of 1.00 upvote
Yeah interactive maps provide lots of options.
For those on Android, there's an app called Bus Finder which does this - it combines Melway maps with bus stop data and timetable/real time info. https://play.google.com/store/apps/details?id=com.rockgecko.busfinder&hl=en
I'm interested. I'm the developer of Bus Finder, which uses the current PTV API to plot bus routes on a map to see where they go. It's part discovery, part trip planning. It used to just plot routes by drawing straight lines between the lat/long of each stop in the run, but since the GTFS data was released, I've added proper paths that follow the road (using shapes.txt)