I use the ATTEN ADS1102CAL, but any 'scope with 20mhz or more bandwidth would be sufficient to do the testing. Not much I do on the bench taxes the 100mhz bandwidth of mine. You can probably pick up a decent 'scope for not much money if all you are interested in is using it around model train electronics. Here's a decent one that's similar to mine, $245 shipped.
Hantek DSO5102P USB Digital Storage Oscilloscope 2 Channels 100MHz 1GSa/s