If you put those last in the chain and go out of both outputs to both amps, you'll hear the effects in stereo. You could go into the mono input in either one, then run the two outputs into the two inputs of the other one.
The real fun for me is having different effects per side - running different drives, delays, reverbs, etc, and even having pitch effects on just one side for a more convincing dual guitar effect. You could put one of these earlier in your chain and try running stuff after it into one amp only. The drawback there is, at least for me, I don't like tremolo or chorus before my main distortion so it would be a bit limiting. You could get a dedicated splitter pedal (I would recommend something active instead of a passive ABY) and not have to worry about that. If you start trying different pedals per side, keep an ear out for phase issues.
I really love the HX Effects for this. It's easy as pie to set up and reorder parallel signal paths for dual outputs, and being able to combine different effects on a single switch means you can minimize tap dancing.